LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


THE  BLAST  FURNACES 

THE  MANUFACTURE 

OF  PIG  IRON 


An  Elementary  Trea- 
tise for  the  use  of  the 
Metallurgical  Student 
and  the  Furnaceman 


By  ROBERT  FORSYTHE 


SECOND  EDITION 


DAVID   WILLIAMS   COMPANY 

14-16   PARK    PLACE 

NEW  YORK 

1909 


Copyright  by 
DAVID  WILLIAMS  CO. 

1908 


To  the  Memory  of 

N.  A.  H., 
without  whose  aid 

this  volume  might  never  have  been  attempted, 
it  is  loyally  dedicated. 


901 328 


PREFACE. 

The  author  begs  to  say  that  this  volume  is  not  offered  as  an 
exhaustive  treatment  of  the  subject,  but  is  designed  primarily 
for  beginners.  He  feels  that  recent  writers  on  iron  metallurgy 
have  addressed  themselves  too  exclusively  to  those  who  are  al- 
ready well  versed  in  its  mysteries.  As  a  student,  he  sought  in 
vain  for  a  simple  and  concise  statement  of  the  general  principles ; 
as  a  teacher,  he  longed  for  one  to  recommend  to  his  students; 
in  practical  work  he  has  had  to  admit  to  many  ambitious  work- 
men that  there  was  nothing  in  the  literature  of  the  subject  that 
came  within  their  grasp.  For  more  than  a  decade  he  has  felt 
that  there  was  need  of  such  a  treatment  on  lines  essentially  Amer- 
ican, and  now  has  attempted  to  supply  it.  He  is  well  aware  that 
there  are  many  others  better  fitted  to  undertake  the  task.  Their 
failure  to  do  so  is  the  best  possible  reason  for  his  presumption. 

The  Fahrenheit  scale  and  the  British  Thermal  Unit  have  been 
given  preference  in  the  text,  because  they  are  more  frequently 
encountered  in  engineering  writings  in  English,  and  because  data 
in  those  units  are  more  readily  obtained  in  this  country.  The  in- 
sertion of  Centigrade  equivalents  is  more  confusing  than  helpful, 
and  the  change,  if  desired,  is  readily  made. 

The  marginal  references  are  intended  primarily  as  guides  to 
collateral  reading.  They  may  or  may  not  indicate  the  source  of 
authority  for  the  contiguous  statements.  They  may  only  refer 
to  a  discussion  from  another  point  of  view.  Chapter  VII  is  not 
offered  as  a  complete  discussion  of  furnace  design,  but  merely 
as  a  guide  by  which  the  untechnical  furnaceman  may  test  the 
suitability  of  his  equipment.  The  chapter  on  the  uses  of  pig  iron 
is  added  in  the  belief  that  no  manufacturer  can  approach  his  task 
intelligently  unless  he  understands  the  limitations  of  his  product. 
The  brief  review  of  the  principles  of  chemistry  and  physics  ii: 
Appendix  I  is  intended  primarily  for  untechnical  readers,  al- 
though it  is  hoped  that  it  may  serve  to  recall  to  others  the  prin- 
ciples which  underlie  the  heat  calculations  in  Chapter  V. 

The  author  wishes  to  acknowledge  his  indebtedness  to  all  re- 


cent  writers  on  ferrous  metallurgy.  In  drawing  from  their  writ- 
ings, he  has  been  compelled  to  condense  the  expressions,  but  he 
trusts  that  he  has  never  perverted  the  sense.  Besides  thanking 
many  manufacturers  for  information  courteously  furnished,  he 
wishes  to  express  his  gratitude  to  Professor  H.  L.  Smyth,  of  Har- 
vard University,  for  a  careful  review  of  the  chapter  on  Materials 
of  Manufacture;  to  Mr.  Alexander  E.  Outerbridge,  Jr.,  of  Phila- 
delphia, for  a  thorough  reading  of  and  valuable  suggestions  on 
the  parts  relating  to  the  constitution  of  iron  and  its  use  in  mak- 
ing castings ;  to  Mr.  H.  Clyde  Snook,  of  the  Roentgen  Manufac- 
turing Company,  of  Philadelphia,  for  a  review  of  the  thermal  cal- 
culations and  all  the  physical  and  chemical  data;  to  Mr.  F.  W. 
Gay,  Mechanical  Engineer  of  the  J.  G.  White  Company,  of  New 
York,  for  a  revision  of  the  section  on  power  development. 
Thanks  are  especially  due  to  Mr.  F.  F.  Amsden,  Furnace  Man- 
ager of  the  Central  Iron  and  Steel  Company,  of  Harrisburg,  Pa., 
the  value  of  whose  many  suggestions  and  patient  revision  of  all 
parts  pertaining  to  the  design,  construction  and  operation  of  the 
furnace  it  would  be  impossible  to  overstate. 

R.  F. 
PHILADELPHIA,  March,  1907. 


ROBERT  FORSYTHE. 

Robert  Forsythe  was  born  at  Braintree,  Massachusetts,  on 
September  5,  1869.  He  graduated  from  Harvard  University  in 
the  class  of  1894,  and,  after  receiving  his  Master's  degree  in  1895, 
was  for  three  years  Instructor  in  Metallurgy  at  Harvard.  He  sub- 
sequently had  practical  metallurgical  experience  in  the  Open 
Hearth  and  Blast  Furnace  Departments  of  the  Pennsylvania  Steel 
Company  at  Steelton,  Pa.,  and  the  Tidewater  Steel  Company  at 
Chester,  Pa.  He  died,  after  a  short  illness,  on  May  23,  1907. 

At  the  time  of  the  author's  death,  "  The  Blast  Furnace  and 
Pig  Iron  "  was  in  proof.  It  is  probable  that  he  would  have  made 
various  minor  changes  in  the  text.  These  it  has  been  impossible 
to  make,  but  it  is  believed  that  the  book  is  published  approximately 
as  he  wished.  If  any  slight  slips  of  pen  or  of  calculation  have 
been  overlooked,  the  blame  should  rest,  not  upon  the  author,  but 
upon  the  friend  in  whose  hands  were  placed  the  proofreading 
and  the  final  details  of  the  book.  E.  S. 

July  5,  1907. 


TABLE  OF  CONTEXTS. 

INTRODUCTORY.  PAGE. 

Commercial  Classification  of  Iron 15 

CONSTITUTION  OF  PIG  IRON 18 

Carbon 18 

Silicon  23 

Manganese  26 

Phosphorus 27 

Sulphur  29 

Aluminum 31 

Other  Elements 31 

PHYSICAL  PROPERTIES  OF  CAST  IRON 32 

Influence  of  Heat  on  Cast  Iron 32 

Strength  of  Cast  Iron 35 

Testing  Cast  Iron 35 

CHAPTER  I.     MATERIALS  OF  MANUFACTURE. . .  39 

ORES  OF  IRON 39 

Constitution  of  Iron  Ores 40 

Nomenclature  of  Iron  Ores 40 

Physical  Condition  of  Ores 43 

Valuation  of  Ores 43 

Relative  Value  of  Ores 47 

PREPARATION  OF  ORES 50 

Calcination 50 

Roasting  52 

Concentration  55 

Agglomeration 61 

Ores  of  the  United  States 62 

FUEL 69 

Constitution  of  Fuels 70 

Natural  Fuels 73 

Prepared  Fuels 74 

Fuel  Consumption  in  the  United  States 84 

Fuel  Analyses 85 

Valuation  of  Fuels 85 

FLUXED  .  86 


Blast  Furnace. 

CHAPTER  II.     DESCRIPTION  OF  PLANT 90 

THE  FURNACE 90 

Furnace  Construction 93 

Furnace   Openings 96 

Top  Arrangements 99 

Hot  Blast  Stoves 109 

Pyrometry 122 

The  Cast  House 125 

The  Boiler  Plant 126 

Blowing  Engines 126 

CHAPTER  III.     OPERATION  OF  THE  FURNACE.  .  ooo 

BLOWING  IN 133 

METHODS  OF  HANDLING  PRODUCTS 136 

Casting  in  Pig  Beds 136 

Casting  in  Ladles 137 

Pig  Casting  Machines 139 

Sample  for  Analysis 141 

Skimming  the  Iron 142 

Cinder  or  Slag 144 

Charging  the  Furnace 148 

Operation  of  Stoves 151 

Interruptions  in  Working 152 

CHAPTER  IV.     BURDENING  THE  FURNACE 156 

SLAG 157 

CONTROL  OF  HEARTH  TEMPERATURE 167 

BURDENING  THE  FURNACE 168 

The  Theoretical  Phase 168 

The  Empirical  Phase 174 

CHAPTER  V.     ACTION  WITHIN  THE  FURNACE. .  182 

THE  DESCENDING  CURRENT  OF  SOLIDS. 182 

THE  ASCENDING  CURRENT  OF  GASES. 184 

INTERACTION  OF  THE  CURRENTS 188 

THE  CARBON  RATIO 193 

CHEMICAL  REACTIONS 195 

HEAT  DEVELOPMENT  IN  THE  FURNACE 197 

HEAT  REQUIREMENTS 206 

REDUCTION  OF  METALLOIDS 218 

CYANIDES .222 


Blast  Furnace. 

ANOMALIES  IN  GAS  COMPOSITION 224 

REDUCTION  BY  CHARCOAL 225 

SOURCES  OF  ECONOMY 227 

CHAPTER  VI.     FURNACE  IRREGULARITIES 234 

LEAKY  TUYERES 234 

DESTRUCTION  OF  LINING 237 

OBSTRUCTIONS  239 

CHILLED  HEARTH 244 

CHAPTER  VII.     HINTS  ON  DESIGN  AND  EQUIP- 
MENT  248 

FURNACE  DESIGN 248 

STOVE  DESIGN 261 

BLOWING  ENGINES 267 

POWER  REQUIREMENT 275 

BOILERS   279 

PUMPS  279 

GAS  ENGINES 280 

GAS  WASHING 283 

ROLLING  STOCK 285 

SUPPLEMENT. 

USES  OF  PIG  IRON 287 

GRADES  OF  PIG  IRON 287 

CONVERSION  OF  PIG  IRON 287 

Wrought  Iron  Conversion 288 

Steel  Conversion 293 

Bessemer  Process 294 

Acid  Open  Hearth  Process 298 

Basic  Open  Hearth  Process 301 

Basic  Bessemer  Process 304 

NON-CONVERSION  IRONS 307 

Gray  Iron  Castings 307 

Purchase  Specifications  for  Foundry  Irons 310 

Chilled  Castings 318 

Toughened   Castings 319 

Effects  of  Molding 320 

Malleable  Castings 321 


Blast  Furnace. 

APPENDIX  I. 

SOME       PRINCIPLES       OF       CHEMISTRY       AND 

PHYSICS 327 

CHEMICAL  CHANGES  IN  MATTER 327 

NATURE  OF  MATTER 328 

Elementary  Substances 328 

Compounds 330 

Oxidation  and  Reduction .  , 331 

Heat  of  Combustion 333 

Combination  of  Oxides 334 

Reducing  Agents 334 

Description  of  Certain  Elements 335 

Oxygen   335 

Nitrogen   336 

Hydrogen   337 

Carbon 338 

Iron 341 

Silicon   341 

Aluminum 342 

Calcium 342 

Manganesium 343 

Manganese   343 

The  Alkalis 344 

Phosphorus 344 

Sulphur 345 

PHYSICAL  CHANGES  OF  MATTER 346 

Phases  of  Matter 347 

The  Phase  Law 347 

The  States  of  Matter 348 

Heat  of  Physical  Changes 351 

Moisture  in  the  Atmosphere 352 

Fixed  Gases 354 

Laws  of  Gases 355 

Heat ' 358 

Fuel   359 

INDEX 366 


OF     '  -r\/ 

UNIVERSITY 


THE   BLAST  FURNACE   AND 

THE    MANUFACTURE 

OF   PIG   IRON 


Introductory. — Iron  is  the  most  abundant  metal  of  this 
planet.  In  the  form  of  some  of  its  various  compounds  it  is  a 
constituent  of  practically  all  rocks  and  earths  and  is  even  found 
associated  with  many  organic  growths.  This  wide  distribution 
has  much  significance  to  the  geologist  and  mineralogist,  but  the 
interest  of  the  metallurgist  is  necessarily  confined  to  those  deposits 
which  are  sufficiently  concentrated  for  the  iron  to  be  extracted  at 
a  profit.  Such  concentrations  are  known  as  ore  bodies,  and 
they  are  the  ultimate  sources  of  all  ferrous  products. 

COMMERCIAL   CLASSIFICATION    OF   IRON. 

All  of  the  iron  of  commerce  may  be  classed  under  three  gen- 
eral heads,  namely :  Cast  iron,  wrought  iron  and  steel.  This  dis- 
tinction is  based  upon  the  physical  characteristics  of  each  class,  as 
influenced  by  the  presence  in  composition  of  certain  non-terrous 
elements.  These  three  classes  glide  almost  imperceptibly  into 
each  other  through  various  intermediary  forms  which  vary  in 
accordance  with  the  composition.  It  is  well,  therefore,  to  under- 
stand these  basal  forms  in  their  original  simplicity  before  pro- 
ceeding to  the  consideration  of  the  more  complex. 

The  occurrence  of  non-ferrous  elements  in  commercial  iron  is 
largely  accidental.  It  is  due  to  their  incomplete  elimination  from 
the  materials  from  which  the  iron  is  made.  The  elements  which 
are  almost  invariably  present  in  all  classes  of  ferrous  products  are 
five  in  number,  namely,  carbon,  silicon,  manganese,  phosphorus 
and  sulphur.  In  addition  to  these,  rarer  elements,  such  as  arsenic, 
titanium,  chromium,  etc.,  are  sometimes  found.  These  elements 
occur  alike  in  all  classes  of  ferrous  products,  so  that  the  above 

15 


16  Blast  Furnace. 

distinctions  are  based  not  on  the  character  of  the  accessions  but 
on  the  degree. 

The  iron  of  commerce  is  never  pure.  That  form  which  usually 
contains  the  least  foreign  elements  is  wrought  iron.  Each  ele- 
ment may  comprise  only  a  trace,  or  at  most,  only  a  few  tenths  of 
a  per  cent,  of  the  whole.  The  sum  of  all  five  may  not  reach  one- 
half  of  one  per  cent.  Such  small  quantities  have  little  effect  upon 
the  properties  of  the  metal,  hence  wrought  iron  may  be  said  to 
exemplify  the  unalloyed  element. 

The  peculiarities  which  distinguish  wrought  iron  from  cast 
iron  and  steel  are  as  follows :  It  is  softer  and  has  a  fibrous  struc- 
ture ;  it  is  extremely  malleable  and  ductile ;  it  has  a  higher  melting 
point,  and  before  the  temperature  reaches  the  melting  point  the 
metal  passes  through  a  plastic  condition  in  which  two  pieces  may 
be  firmly  united  by  the  process  of  welding.  The  presence  of  for- 
eign elements  modifies  all  of  these  properties.  It  lowers  the  melt- 
ing point,  increases  the  hardness,  imparts  a  crystalline  structure, 
and  interferes  with  the  malleable  properties  and  the  power  of 
welding. 

The  ferrous  product  which  most  nearly  resembles  wrought 
iron  is  steel.  Its  composition  differs  from  that  of  wrought  iron  in 
only  one  particular :  it  may  contain  more  carbon.  It  may  even  be 
made  from  wrought  iron  by  the  addition  of  carbon  alone — the 
other  elements  remaining  unchanged.  The  amount  of  carbon 
which  steel  may  contain  usually  ranges  from  a  few  hundredths 
per  cent,  up  to  2  per  cent,  or  more.  Its  properties  vary  with 
its  composition.  When  the  content  of  carbon  is  low,  it  possesses 
the  properties  of  wrought  iron.  It  melts  with  difficulty ;  it  is 
ductile  and  malleable;  it  is  soft  and  may  be  welded.  As  the 
proportion  of  carbon  increases,  these  properties  pass  through 
gradual  changes.  The  melting  point  falls ;  the  metal  becomes 
harder  and  more  resistant  to  pressure  and  changes  of  form,  and 
the  welding  property  gradually  disappears.  In  addition,  an  en- 
tirely new  property  appears,  namely,  the  power  to  become  in- 
tensely hard  when  cooled  suddenly  from  high  temperatures. 
These  characteristics  become  more  marked  with  each  addition  of 
carbon.  The  final  product  is  a  substance  that  is  hard  and  brittle, 
and  in  every  way  different  from  the  tough,  fibrous,  wrought  iron. 


Introductory. 


17 


The  third  member  of  the  series  is  cast  iron,  whose  composition 
differs  from  that  of  the  other  two  only  in  degree.  The  proportion 
of  non-ferrous  elements  present  in  cast  iron  usually  ranges  from 
5  to  10  per  cent.  The  distribution  of  the  more  usual  elements  is 
as  follows :  Silicon,  usually  under  3  per  cent. ;  carbon,  2^  to 
4l/2  per  cent. ;  manganese,  usually  under  2  per  cent. ;  phosphorus, 
usually  under  I  per  cent.,  and  sulphur,  usually  under  o.i  per  cent. 
Any  or  all  of  these  elements  except  carbon  may  be  reduced  to  a 
mere  trace  without  declassifying  the  substance.  It  is  evident, 
therefore,  that  the  composition  of  cast  iron,  as  well  as  that  of 
steel,  is  variable;  indeed,  it  is  subject  to  a  much  wider  variation. 
If  we  assume  that  all  of  the  above  elements  be  eliminated  from  a 
low  carbon  cast  iron,  we  would  have  a  substance  that  could  be 
equally  well  classified  as  a  very  high  carbon  steel.  A  compara- 
tively slight  elimination  of  carbon  would  then  produce  a  metal 
suitable  for  high  grade  steel  instruments.  Plainly,  then,  cast  iron 
is  but  the  completion  of  the  series  which  was  begun  by  wrought 
iron  and  continued  by  steel.  The  continuousness  of  the  composi- 
tion and  properties  of  this  series  is  illustrated  by  the  following 
diagram  by  Howe. 


STEEL 


CAST   IRON 


160000 


1.5     2.0     2.5 
PERCENT  CARBON 

Howe's   Diagram    Illustrating   the   Composition   and    the    Properties   of   the    Iron 

Series. 

The  properties  of  cast  iron,  with  its  accumulation  of  non- 
ferrous  elements,  could  not  be  other  than  very  different  from 
those  of  the  comparatively  pure  wrought  iron.  Since  it  is  at  the 


Am.  Soc.; 
Test.  Mat. 
II,  p.  246. 


18  Blast  Furnace. 

other  end  of  the  series,  its  behavior  is  qqite  opposite  to  that  of 
wrought  iron.  It  melts  readily  and  passes  suddenly  into  the 
fluid  state;  hence,  it  cannot  be  forged  and  welded.  Indeed,  its 
reluctance  to  change  its  form  without  rupture  is  accentuated 
instead  of  decreased  by  high  temperatures.  It  is  coarsely  crystal- 
line, easily  broken,  and  altogether  different  in  appearance  and 
behavior  from  both  of  its  associates. 

Cast  iron  in  its  cruder  form,  which  is  called  "  pig  iron"  from 
a  fancied  resemblance,  is  the  only  ferrous  product  which  is  now 
produced  from  the  ores  direct.  It  is  a  crude  substance  at  best, 
and  while  certain  varieties  may  be  formed  directly  into  finished 
products,  such  as  castings,  a  very  large  proportion  serves  only 
as  a  starting  point  for  various  processes  of  refining  which  result 
ultimately  in  the  production  of  wrought  iron  and  steel. 

CONSTITUTION  OF  PIG  IRON. 

Since  pig  iron,  in  its  many  forms,  is  made  up  of  varying  pro- 
portions of  several  different  elements,  each  of  which  exerts  cer- 
tain specific  effects  upon  the  appearance  and  properties  of  the 
metal,  it  may  reasonably  be  considered  a  fairly  complex  substance. 
Its  complexity,  however,  does  not  depend  solely  upon  its  variable 
composition,  but  is  affected  also  by  attendant  circumstances.  In- 
itial temperature,  rate  of  cooling,  size,  shape  and  position  are 
some  of  the  conditions  which  will  affect  the  properties  of  iron  of 
any  given  composition,  and  thereby  multiply  infinitely  the  varieties 
possible.  In  order  to  grasp  fully  the  possibilities  of  pig  iron, 
therefore,  it  is  necessary  to  study  its  constitution  in  detail. 

CARBON. 

As  already  stated,  the  only  non-ferrous  element  which  is  abso- 
lutely essential  to  cast  iron  is  carbon.  Yet  pig  iron,  which  con- 
sists of  iron  and  carbon  alone,  is  of  no  practical  value  in  making 
castings.  They  would  be  hard,  correspondingly  brittle,  and  diffi- 
cult to  machine.  Therefore  other  elements  beside  carbon  are 
necessary  to  the  production  of  desirable  castings.  Their  influence, 
however,  is  due,  not  so  much  to  their  action  upon  the  iron,  as  to 
their  effect  upon  the  condition  of  the  carbon. 


Introductory.  19 

Condition  of  Carbon. — As  a  rule  the  total  per  cent,  of  carbon 
in  pig  iron  is  fairly  constant.  It  usually  ranges  from  3*4  to  4 
per  cent,  of  the  whole.  The  variation  in  its  condition,  however, 
may  cover  a  wide  range.  Carbon  is  known  to  exist  in  iron  in  no 
less  than  four  different  forms,  only  two  of  which  it  is  necessary 
to  consider  here.  These  two  forms  are  called  graphitic  carbon 
and  combined  carbon.  Graphitic  carbon  is  that  which  appears 
as  black,  shining  flakes,  readily  distinguishable  on  a  freshly-broken 
surface  of  high-grade  pig  iron.  It  is  practically  pure  carbon, 
which  has  separated  from  the  iron  during  solidification,  and  no 
longer  exerts  any  influence  upon  the  surrounding  metal.  The 
combined  carbon  is  that  portion  of  the  total  carbon  which  still 
remains  in  combination,  or  alloyed  with,  the  iron  which  surrounds 
the  flakes  of  graphite.  It  exerts  a  profound  influence  upon  the 
metal. 

In  general,  pig  iron  may  be  likened  to  a  mass  of  concrete,  in 
that  it  consists  of  particles  of  graphite  surrounded  by  a  matrix  of 
metallic  alloy.  The  proportion  of  carbon  existing  in  each  state  is 
subject  to  wide  variation.  In  some  irons  it  may  exist  as  prac- 
tically all  graphite  with  very  little  combined  carbon ;  in  others 
it  may  be  all  in  the  combined  form  with  little  or  no  graphite. 
Its  condition  is  profoundly  affected  by  the  presence  of  other 
elements  and  also  by  the  rate  of  cooling.  Very  important  dis- 
tinctions in  pig  iron  are  based  upon  -the  ratio  of  graphitic  and 
combined  carbon.  The  presence  of  graphite  g^es  the  'grayish 
black  crystalline  appearance  which  is  characteristic  of  foundry 
irons.  Much  combined  carbon,  on  the  other  hand,  gives  iron  a 
white  or  mottled  appearance  and  renders  it  unsuitable  for  many 
purposes. 

Structure  of  Pig  Iron — The  strength  of  iron  is  greatly  af- 
fected by  the  condition  of  the  carbon.   The  crystals  of  graphite  are 
brittle  and  show  decided  cleavages,  hence  they  cannot  be  a  factor 
of  strength  in  the  iron.     Indeed,  by  breaking  up  the  continuity 
of  the  metallic  matrix,  the  graphite  causes  weakness,  which  will 
vary  directly  with  the  quantity.     The  matrix  is  an  alloy  of  iron    TnA>I.M.E., 
with  carbon  and  other  elements  which  may  be  present.     It  pos-    XXXI-p-31s- 
sesses  properties  varying  with  the  percentage  of  carbon  in  the 
alloy.     Since  all  of  the  strength  of  the  iron  is  due  to  the  metallic 


20  Blast  Furnace. 

matrix,  it  is  evident  that  the  strength  will  vary  in  proportion  to 
the  amount  of  carbon  entering  into  the  matrix.  It  appears,  then, 
that  carbon  affects  the  strength  of  iron  in  two  ways :  ( i )  in  the 
form  of  graphite  it  weakens,  by  interrupting  the  continuity  of  the 
matrix,  (2)  as  combined  carbon  it  strengthens  by  strengthening 
the  matrix.  This  is  true,  however,  only  up  to  about  i  per  cent, 
of  combined  carbon.  Further  quantities  tend  to  weaken  the 
matrix.  The  explanation  of  this  reversal  of  the  effect  of  carbon 
lies  in  the  structure  of  the  alloy.  Under  the  microscope,  combi- 
nations of  iron  and  carbon,  which  are  formed  under  usual  condi- 
tions, show  a  crystalline  structure  which  may  be  likened  to  that 
of  granite,  and  which  consists  of  two  components.  All  of  the 
carbon  unites  with  iron  in  the  ratio  of  i  :  14  by  weight,  to  form  a 
carbide  of  iron  having  6^  per  cent,  carbon  and  93^5  per  cent. 
Tr.  A.  i.  M.  E.,  iron,  and  approximating  the  chemical  formula  Fe3C,  which  is 
called  Cementite.  This  is  one  component.  The  other  consists  of 
the  free  iron  which  remains  in  excess  of  the  quantity  required  to 
form  Fe3C  with  all  of  the  carbon  present,  and  is  known  as  Fer- 
rite.  The  ferrite  and  cementite  then  proceed  to  unite  in  alternate 
parallel  layers  to  form  a  true  eutectic  alloy,  in  which  they  approxi- 
mate the  proportions  7:1  by  weight.  Under  the  microscope  this 
finely-banded  structure  presents  a  pearly  luster,  and  is  conse- 
quently known  as  Pear  lite.  The  pearlite  crystallizes  in  tolerably 
regular  polygonal  grains,  along  whose  edges  the  excess  of  ferrite 
or  cementite  collects  as  a  network.  Since  cementite  contains 
62/3  per  cent,  of  carbon,  and  unites  to  form  pearlite  with  seven 
times  its  weight  of  ferrite,  it  follows  that  pearlite  must  contain 

—  =  0.85  per  cent,  of  carbon.    It  is  apparent,  then,  that  the 

presence  of  just  0.85  per  cent,  of  carbon  would  produce  a  metal 
consisting  entirely  of  pearlite,  and  it  is  a  necessary  corollary, 
therefore,  that  a  metal  containing  less  than  0.85  per  cent,  would 
consist  of  pearlite  and  a  residual  network  of  ferrite.  while  one 
containing  more  than  0.85  per  cent,  of  carbon  would  consist  of 
pearlite  and  a  residual  network  of  cementite.  Since  pearlite  is 
a  very  strong  substance,  the  natural  planes  of  weakness  in  such 
a  metal  would  be  along  the  lines  of  network.  Ferrite,  being  pure 
iron  and  naturally  tough  in  consequence,  would  offer  more  re- 


Introductory.  21 

sistance  to  cleavage  than  cementite,  which  is  a  hard  crystalline 
substance.  This  fact  explains  why  a  matrix  containing  less  than 
i  per  cent,  combined  carbon  is  stronger  than  one  containing  more 
than  i  per  cent.  The  proportions  of  ferrite,  cementite  and  pearl- 
ite, and  the  excess  of  ferrite  or  cementite  over  that  needed  to  form 
pearlite  with  all  of  the  carbon  present,  are  shown  by  the  follow- 
ing table  for  various  percentages  of  carbon : 

Excess 


Carbon. 

Ferrite. 

Cpmentite. 

Pearlite. 

Excess  ferrite. 

cementite. 

0.0 

100.0 

0.0 

0.0 

100.0 

0.0 

0.1 

98.5 

1.5 

12.0 

88.0 

0.0 

• 

0-2 

97.0 

3.0 

25.0 

75.0 

0.0 

0.3 

95.5 

4.5 

37.0 

63.0 

0.0 

0.5 

92.5 

7.5 

62.0 

38.0 

0.0 

Am.  Soc. 

0.7 

89.5 

10.5 

87.0 

13.0 

0.0 

Test.  Mat 

0.85 

87.8 

12.2 

100.0 

0.0 

0.0 

II,  p.  246. 

1.0 

85.0 

15.0 

97.0 

0.0 

3.0 

1.5 

77.5 

22.5 

88.0 

0.0 

12.0 

2.0 

70.0 

30.0 

80.0 

0.0 

20.0 

2.5 

62.5 

37.5 

71.0 

0.0 

29.0 

3.0 

55.0 

45.0 

62.5 

0.0 

37.5 

3.5 

47.5 

52.5 

54.0 

0.0 

46.0 

4.0 

36.25 

63.75 

45.5 

0.0 

54.5 

Strengthening  Effect  of  Carbon — From  these  considerations 
it  appears  that  a  change  in  the  condition  of  carbon  may  sometimes 
strengthen  and  sometimes  weaken  the  iron.  For  example,  an  iron 
containing  3'^  per  cent,  graphite  and  l/±  per  cent,  combined  car- 
bon would  have  a  highly  interrupted  matrix  which  contains  but 
little  of  the  strengthening  pearlite.  Any  change  of  graphite  to 
combined  carbon  would  make  the  matrix  more  continuous  and  at 
the  same  time  increase  the  pearlite.  Both  factors  contribute 
strength.  The  maximum  strength  would  probably  be  reached 
when  there  was  2^4  Per  cent,  graphite  and  i  per  cent,  combined 
carbon.  A  further  change  of  graphite  to  combined  carbon 
would  tend  to  increase  continuity  of  matrix,  but  would  introduce 
weakness  into  the  matrix  itself,  in  the  shape  of  brittle  cementite. 
The  weakening  effect  of  cementite  overbalances  the  strengthening 
effect  of  increased  continuity  and  the  net  result  is  a  loss  of 
strength.  Further  change  in  this  direction  only  tends  to  aggra- 
vate the  weakness  through  the  introduction  of  still  larger  masses 
of  the  brittle  cementite.  These  effects  may  be  masked,  however, 
by  other  conditions  or  the  presence  of  other  elements,  but  it  is 


22  Blast  Furnace. 

very  evident  that  the  strongest  iron,  as  far  as  carbon  is  concerned, 
will  be  the  one  which  contains  about  i  per  cent,  of  combined  car- 
bon, and  the  least  possible  graphite.  This  statement  is  well 
borne  out  by  experience  and  is  well  illustrated  by  analyses  selected 
from  experiments  by  Johnson  : 

Total  Graph.  Comb.  T  S.,  Ibs.     Character  of 

Si.  P.  C.  C.  C.  persq.  in.        fracture. 

IntasJ°Ii;;     1-20          O.OGG          0.173          3.87          3.72          0.15          17,500      Very  open  grain. 

P.  210.     1.21          0.067          0.179          3.85  3.52          0.33          22,400       Bright  open  grain. 

1.20  O.OGG          0.170          3.82  3.42          0.40          24,550      Bright  close  grain. 

1.21  0.061          0.174          3.88  2.95          0.93          33,850       Very  close  grain. 

Since  these  irons  are  remarkably  uniform  in  composition,  we 
can  attribute  their  change  in  strength  and  texture  only  to  the 
change  in  condition  of  the  carbon. 

Absorption  of  Carbon. — Carbon  may  be  taken  up  by  iron  in 
two  ways.  It  is  very  readily  dissolved  by  molten  iron,  and  it  is 
also  more  or  less  actively  absorbed  by  the  solid  metal  at  all  tem- 
peratures above  redness.  The  dissolving  of  carbon  by  molten 
iron  up  to  the  saturation  point  is  practically  instantaneous.  On 
the  other  hand,  the  rate  of  absorption  of  the  solid  iron  and  its 
capacity  for  carbon  depend  upon  the  temperature.  The  quantity 
absorbed  at  a  given  temperature  depends  also  upon  the  time 
allowed.  The  actions  of  these  two  methods  of  uniting  carbon 
end  iron  are  well  illustrated  by  experiments  by  E.  H.  Saniter. 
He  melted  some  pure  iron  wire  in  a  crucible  with  an  excess  of  car- 
bon and  found  that  the  iron  absorbed  4.73  per  cent,  of  its  weight 
of  carbon.  He  heated  some  of  the  same  wire  in  a  porcelain  tube 
Inm7°n"  which  was  packed  full  of  powdered  charcoal,  and  held  it  at  a 
P.  119.  temperature  of  1650  degrees  F.  At  the  end  of  7  hours  it  con- 
tained 1.64  per  cent.  C.,  at  the  end  of  14  hours  it  contained  2.79  per 
cent.  C.,  at  the  end  of  21  hours  it  contained  2.95  per  cent.  C, 
which  was  probably  reasonably  close  to  the  saturation  point  for 
that  temperature. 

Carbon  and  Other  Elements. — The  quantity  of  carbon  that 
may  be  dissolved  by  molten  iron,  and  the  state  in  which  the  dis- 
solved carbon  will  exist  after  cooling,  are  both  affected  profound- 
ly by  the  presence  of  other  elements.  Silicon,  for  example,  changes 
combined  carbon  to  graphitic.  It  also  tends  to  exclude  carbon. 


Introductory.  23 

An  iron  containing  3  per  cent,  silicon  usually  contains  3  to  4  per 
cent,  carbon.  With  10  per  cent,  silicon,  not  more  than  2  per  cent, 
carbon  may  be  present,  and  with  20  per  cent,  silicon,  the  carbon 
is  nearly  or  wholly  absent.  On  the  other  hand,  manganese  and 
chromium  raise  the  saturation  point  of  iron  for  carbon,  and  tend 
also  to  keep  it  in  the  combined  state.  The  presence  of  75  per  cent, 
manganese  permits  the  solution  of  about  7  per  cent,  carbon,  inst.jour., 
while  a  similar  proportion  of  chromium  will  raise  the  saturation  p.  235. ' 
point  above  10  per  cent.  These  figures  represent,  however,  more 
nearly  the  dissolving  power  of  manganese  and  chromium  than 
that  of  the  iron,  as  the  percentage  of  iron  in  such  metals  is  com- 
paratively insignificant.  In  irons  containing  both  silicon  and 
manganese,  such  as  the  silico-spiegel  series,  these  elements  ap- 
pear to  share  the  honors.  Silicon  continues  to  exclude  carbon, 
though  not  as  rapidly  as  when  alone,  but  the  ratio  of  combined 
carbon  to  graphite  is  higher  than  in  ordinary  irons.  The  follow- 
ing analyses  by  W.  J.  Keep  illustrate  the  effect  of  silicon  upon  the 
quantity  and  condition  of  carbon  in  cast  iron : 


Si 

0.18 

1.25 

2.03 

3.15 

4.39 

5.89 

9.10 

10.34 

12.08 

16.27 

T. 
G. 
p 

C..  . 
C..  . 

.  .2.53 
.  .  0.49 
0.126 

3.55 
3.22 
0.08 

3.75 
3.12 
1.65 

3.50 
2.46 
1.06 

3.44 
3.40 
1.42 

3.15 
2.85 
1.10 

"2.58 
0.90 
0.09 

1.99 
1.92 
0.48 

1.58 
1.52 

0.48 

0.75 
0.01 

g 

0  03 

0.04 

0.01 

0.02 

Tr. 

0.02 

0.03 

Tr. 

Tr. 

0.01 

Mn 

.  .  0.09 

0.18 

0.87 

1.35 

1.00 

2.20 

0.57 

0.76 

0.60 

20.00 


W.  J.  Keep. 
Cast  Iron, 
1st  Ed. 


SILICON. 

Silicon  appears  to  be  able  to  unite  with  iron  in  all  proportions. 
Pig  irons  containing  quantities  of  silicon  ranging  from  a  few 
tenths  per  cent,  up  to  5  per  cent,  are  made,  at  least  occasionally, 
at  all  blast  furnaces.  Ferro-silicon  containing  12  per  cent,  sili- 
con is  a  regular  blast  furnace  product.  By  means  of  the  electric 
furnace  the  percentage  may  be  raised  to  60  or  80  per  cent. 

Effects  of  Silicon. — The  effect  upon  iron  of  small  percentages 
of  silicon  is  usually  masked  by  that  of  carbon.  In  the  presence 
of  high  percentages,  however,  carbon  is  practically  excluded  and 
the  resulting  metal  is  hard  and  brittle.  It  is  probable,  then,  that 
silicon,  even  in  small  quantities,  is  really  a  hardening  agent,  but 
owing  to  its  effect  upon  the  condition  of  carbon,  usually  appears 
to  be  a  softener.  Analyses  by  Johnson  appear  to  indicate  that 


24  Blast  Furnace. 

when  other  conditions  are   constant,   silicon  materially   weakens 
iron: 


Inst.  Jour., 
1398,  II., 

T.  S.,  Ibs. 

Character  of 

Table  III.      T.  C. 

G.  C. 

C.  C. 

P. 

S. 

Si. 

per  >•<].  in. 

fracture. 

3.82 

3.03 

0.79 

0.179 

0.071 

•    0.31 

31,550 

Gray 

fracture. 

3.83 

2.98 

0.85 

0.178 

0.070 

1.1:7 

29,050 

Gray 

fracture. 

3.90 

3.07 

0.83 

0.179 

0.007 

1.7G 

22,850 

Gray 

fracture. 

3.81 

3.01 

0.80 

0.179 

0.073 

2.03 

19,G50 

Gray 

fracture. 

Even  in  small  percentages  silicon  appears  to  exclude  carbon 
from  iron.  Pure  iron  has  a  capacity  for  carbon  up  to  4.7  per  cent, 
of  its  own  weight  when  melted  at  the  highest  temperatures.  Irons 
containing  2  to  3  per  cent,  silicon  and  made  at  normal  furnace 
temperature  rarely  contain  over  3.5  to  4  per  cent,  of  carbon,  which 
shows  the  exclusion  of  nearly  or  quite  I  per  cent,  of  carbon. 
Low  silicon  irons  also  rarely  show  over  4  per  cent,  of  carbon. 
This  fact  may  be  accounted  for  by  the  low  temperature  of  forma- 
tion of  such  irons. 

In  quantities  exceeding  about  4  per  cent.,  silicon  gives  to  pig 
iron  a  peculiar  glazed  appearance,  accompanied  by  increasing 
weakness,  which  unfits  it  for  castings.  The  silicon  in  foundry 
irons  does  not  usually  rise  above  3  per  cent.,  and  for  most  pur- 
poses 2  per  cent,  is  better.  Xo  exact  rule  can  be  given  for  de- 
termining the  best  percentage  of  silicon  for  given  results,  because 
its  influence  depends  upon  its  power  to  control  the  ratio  of 
graphitic  and  combined  carbon,  while  the  strength  of  the  iron,  as 
we  have  seen,  depends  mostly  upon  the  quantity  of  combined  car- 
bon. Since  silicon  affects  only  the  proportion  of  the  total  car- 
bon which  remains  in  combination  with  the  iron,  it  is  evident 
that  the  quantity  so  uniting  will  depend  upon  the  total  amount 
of  carbon  present.  This  quantity  is  materially  affected  not  only 
by  the  silicon  present,  but  also  by  the  temperature  of  formation 
and  the  presence  of  other  elements.  It  is  evident,  then,  that  the 
Tr' Axxvin.',  proper  quantity  of  silicon  for  certain  results  cannot  be  easily 
p' 769-  predicted,  but  that  it  varies  according  to  the  percentages  of  other 
elements  present. 

Benefits  oi  Silicon. — If  a  casting  were  made  from  pig  iron 
practically  free  from  silicon  it  would  be  found  to  be  hard,  white, 
brittle  and  more  or  less  porous.  The  addition  of  a  small  per- 
centage of  silicon  would  make  the  casting  solid,  and  thereby  add 


Introductory.  25 

to  its  strength.  Further  addition  of  silicon,  say  i  per  cent.,  would 
turn  the  iron  from  white  to  a  fine-grained  gray  color,  and  in- 
crease the  softness  and  strength.  Still  further  additions,  up  to 
3  per  cent.,  would  enlarge  the  grain  and  increase  the  softness 
without  materially  decreasing  the  strength.  Silicon  up  to  0.9 
per  cent,  usually  increases  the  strength  of  all  sizes  of  castings. 
When  it  exceeds  i  per  cent,  it  tends  to  decrease  the  strength 

^  Am.  Soc. 

of  all  sections  over  I  inch  square.  Up  to  2  per  cent,  it  strengthens  J^*1*1- IV- 
all  sections  under  i  inch  square,  and  up  to  3  per  cent,  it  strength- 
ens sections  of  l/2  inch  square.  Above  5  per  cent,  of  silicon  the  color 
becomes  lighter,  the  hardness  returns  rapidly,  and  the  strength  is 
soon  changed  to  brittleness.  In  general,  it  may  be  stated  that 
up  to  about  3  per  cent.,  silicon  is  increasingly  beneficial,  since  it 
promotes  soundness,  softness  and  strength,  and  decreases  shrink- 
age and  chilling  properties.  These  effects  are  the  result  of  chang-  ^r^  I-pM71f •• 
ing  combined  carbon  to  graphite,  in  accordance  with  the  law  that 
combined  carbon  usually  varies  inversely  with  the  quantity  of 
silicon.  This  effect  is  not  always  proportionate,  however,  as  iron 
appears  to  be  more  sensitive  to  change  in  silicon  when  it  is  below 

1  per  cent,  than  when  above.     By  the  addition  of  silicon  to  white 
iron  when  molten,  practically  worthless  iron  may  be  turned  to 
good  account.      However,   carbon  has  a  tendency   to   retain   its 
original  condition,  so  it  may  happen  that  a  given  percentage  of   xvn'p 
added  silicon  may  not  produce  the  same  result  as  if  the  silicon 

had  been  originally  present  in  the  pig.  When  enough  silicon  has 
been  added  to  give  soundness,  even  while  the  iron  is  still  hard 
and  brittle,  it  offers  its  highest  resistance  to  compressive  forces. 
At  that  time,  also,  it  exhibits  its  maximum  specific  gravity. 
When  the  addition  of  silicon  begins  to  cause  the  separation  of 
graphite,  the  transverse  strength  reaches  its  maximum.  The 
greatest  tensile  strength  is  reached  when  the  silicon  rises  toward 

2  per  cent.     Deflection  follows  strength  closely,  and  shrinkage 
follows  hardness.     The  ideal  compositions  recommended  by  Tur- 
ner are : 

Per  cent.  Si. 

Maximum  hardness,  under 0.80    j  c  S 

Maximum  crushing  strength,  about 0.80     1885, 

Maximum  transverse  strength,  about 1.40    pp'    ' ' 

Maximum  tensile  strength,  about 1.80 

Maximum  softness,  about 2.50 


26  Blast  Furnace. 

In  addition  to  its  beneficial  effect  upon  carbon,  silicon  im- 
proves cast  iron  in  two  ways;  it  tends  to  exclude  sulphur  and  it 
prevents  blow  holes.  Irons  which  are  high  in  silicon  are  gen- 
erally low  in  sulphur.  This  is  probably  largely  due  to  the  vola- 
tilization of  the  sulphur  by  the  high  temperature  necessary  to 
produce  high  silicon  irons.  The  action  of  silicon  in  promoting 
soundness  by  preventing  blow  holes  is  not  clearly  understood. 
Blow  holes  are  caused  by  the  gases  which  are  always  in  solution 
in  the  molten  iron  and  which,  set  free  during  the  cooling,  become 
entangled  in  the  rapidly  solidifying  metal.  The  presence  of  the 
silicon  either  prevents  the  dissolving  of  the  gases  in  the  first  place 
or  else  it  enables  them  to  stay  in  solution  in  the  solid  metal.  The 
latter  explanation  is  the  one  usually  accepted. 

MANGANESE. 

Manganese  can  alloy  with  iron  in  all  proportions.  Up  to 
about  i  per  cent,  it  does  not  appreciably  affect  the  properties  of 
cast  iron.  In  larger  proportions  it  increases  the  hardness  of 
the  iron  and  also  its  capacity  for  carbon.  Unlike  silicon,  however, 
it  tends  to  keep  the  carbon  in  the  combined  state.  Therefore  it 
can  harden  the  iron  in  two  ways :  by  its  own  effect,  and  by  its 
influence  upon  the  condition  of  the  carbon.  As  the  proportion 
of  manganese  rises,  hardness  and  brittleness  increase.  Between 
10  and  30  per  cent,  manganese  gives  a  hard,  white,  brittle 
substance,  which  shows  large  crystal  facets  on  the  fractured  sur- 
face. This  is  known  as  spiegeleisen,  and  is  made  regularly  for 
use  in  steel  making.  It  is  wholly  unsuitable  for  making  castings. 
Irons  containing  higher  percentages  of  manganese  are  known  as 
ferromanganese.  They  usually  contain  as  high  as  80  per  cent. 
Mn.,  and,  like  Spiegel,  are  used  chiefly  in  steel  making.  Their 
grain  is  close  and  the  fracture  granular,  frequently  showing 
beautiful  iridescent  colors.  They  are  so  brittle  as  to  be  easily 
pulverized. 

Effects  of  Manganese. — In  small  quantities  manganese  is  un- 
doubtedly beneficial  to  cast  iron.  Less  than  I  per  cent,  does  not 
cause  a  material  increase  in  hardness.  Indeed,  it  may  act  as  a 
softener  of  certain  kinds  of  hard  iron.  This  is  due  to  its  power 
of  uniting  with  sulphur  to  form  a  sulphide  of  manganese  which 


Introductory.  27 

separates  from  the  metal.  Hence,  an  iron  whose  hardness  is 
due  to  the  presence  of  sulphur  may  be  softened  by  the  addi- 
tion of  manganese.  It  is  therefore  particularly  beneficial  to  irons 
which  do  not  have  much  silicon,  as  it  keeps  the  sulphur  low.  Its 
presence  tends  also  to  prevent  the  absorption  of  sulphur  from  the 
fuel  during  remelting.  The  affinity  of  manganese  for  sulphur  inst.jour., 
forms  the  basis  of  a  process  of  desulphurization-of  molten  pig  iron.  i«- 70- 

In  quantity  exceeding  i  per  cent.,  manganese  is  likely  to  be 
detrimental  to  cast  iron,  partly  because  of  its  tendency  to  in-   is»8,". 
crease  the  percentage  of  carbon,  and  to  keep  it  in  the  combined 
state,  thereby  tending  to  make  the  iron  white,  and  partly  because 
of  its  own  power  to  confer  hardness.    Hardness,  from  any  cause, 
is   followed   by  a   train   of  evils,   such   as  brittleness,   increased 
shrinkage  and  difficulty  in  machining.      In  remelting,  manganese 
is  readily  oxidized  and  lost  from  the  iron,  so  that  the  content  of 
the  pig  cannot  be  safely  counted  on  in  the  castings.     The  effect   IronAge) 
of  manganese  on  the  condition  of. carbon,  the  quantity  of  sulphur,  pu£o5f9' 190o> 
and  chill  is  illustrated  below: 


SI. 

P. 

T.C. 

Mn. 

C.C. 

S. 

Chill. 

0.55 

0.22 

3.67 

1.38 

0.62 

0.048 

2.00  inches. 

0.49 

0.25 

3.72 

2.00 

0.74 

0.030 

2.25  inches. 

0.49 

0.24 

3.70 

2.25 

1.03 

0.025 

2.30  inches. 

0.74 

0.27 

.  .  . 

3.80 

2.52 

0.020 

All  white. 

PHOSPHORUS. 

Phosphorus  and  Carbon. — Phosphorus  appears  to  be  able  to 
unite  with  iron  in  all  proportions.  It  exercises  a  strong  ex- 
cluding effect  upon  carbon.  Iron  in  combination  with  i^.^S  per  inst.  jour. 

J  J  1900,  II., 

cent,  phosphorus  forms  a  compound  corresponding  to  the  for-  p-109- 
mula  Fe3P,  in  which  carbon  is  absolutely  insoluble.  It  is  evident, 
then,  that  an  iron  containing  about  16  per  cent,  phosphorus  will 
be  carbonless,  and  that  lesser  quantities  of  phosphorus  will  admit 
of  only  a  proportionate  amount  of  carbon.  This  is  shown  by  the 
following  analyses  by  Stead  : 

S1-  P-  T.C.  G.  C.                       C.C.  Mn. 

0.92  0.21  3.72  2.62  1.10  Trace. 

1-96  4.95  2.29  1.73  0.56  Trace. 

1.06  6.85  1.99  1.88  0.11  Trace. 

284  8.35  1.69  1.69  0.00  Trace. 

3-36  12.86  0.83  0.83  0.00  Trace. 


28  Blast  Furnace. 

Since  the  ratios  between  the  graphite  and  the  combined  carbon 
in  this  table  are  about  what  would  be  predicted  from  the  quantity 
of  silicon  present,  it  is  probable  that  phosphorus  does  not  exert  a 
very  strong  influence  upon  the  condition  of  the  carbon,  but  only 
upon  its  quantity. 

Phosphorus  tends  strongly  to  segregate,  and  high  phosphorus 
pig  when  broken  before  the  center  has  solidified  shows  generally 
several  times  as  much  phosphorus  in  the  liquid  portion  as  in  the 
solidified  portion.  This  liquate  is  probably  an  eutectic  alloy  of  the 
elements  present.  The  eutectic  alloy  of  iron  and  phosphorus 
begins  to  appear  in  pig  iron  when  phosphorus  exceeds  about  1.7 
per  cent.  Below  this  point  the  phosphorus  exists  as  the  com- 
pound Fe3P,  which  is  dissolved  in  the  excess  of  iron.  It  is  this 
solution  that  the  presence  of  carbon  tends  to  prevent.  The  iron 
does  not  appear  to  be  able  to  hold  in  solution  both  carbon  and 
Fe3P  independently.  One  must  always  be  sacrificed  for  the  other. 
This  struggle  for  the  possession  of  the  iron  is  illustrated  by  the 
following  analyses  bv  Stead  : 

c. 

0.00 

Inst.  Jour.,  n  i  fi 

1900,  II. 

p.  84.  0.70 

1.40 
3.50 

Effect  on  Strength. — The  Fe3P,  thus  set  free,  forms  an  eutec- 
tic with  the  other  elements  not  in  solution,  which  then  combines 
with  the  pearlite  to  form  a  phospho-pearlite  eutectic  containing 
0.6  per  cent.  P.  Any  excess  of  Fe3P  collects  along  the  junctions 
of  the  grains  and  causes  brittleness  in  high  phosphorus  irons. 
This  tendency  is  greatly  lessened  by  the  fact  that  the  phosphorus 
compounds  tend  to  collect  in  globular  form  instead  of  completely 
enveloping  the  grains.  This  distribution  leaves  considerable 
areas  of  strong  metal  between,  and  postpones  the  appearance  of 
the  weakness  until  the  amount  of  phosphorus  causes  such  large 
globules  that  the  strong  ground-mass  is  materially  lessened.  This 
condition  is  reached  at  approximately  1.7  per  cent.  The  weaken- 
ing effect  of  phosphorus  is  largely  neutralized  by  the  presence 
of  titanium.  The  titanium  increases  the  total  carbon  and  makes 


P  in  Fe3P, 

Pin 

Total  P. 

dissolved  in  iron. 

free  FezP. 

1.75 

1.75 

0.00 

1.77 

1.18 

0.59 

1.75 

0.75 

1.00 

1.76 

0.60 

1.16 

1.71 

0.31 

1.40 

Introductory.  29 

it  mostly  graphitic.  It  is  claimed  that  l/2  per  cent,  of  titanium  will 
give  strength  to  iron  containing  3  per  cent,  phosphorus.  Phos- 
phorus causes  pig  iron  to  have  an  enlarged  grain  with  a  yellowish 
color.  It  does  not  affect  the  shape  of  the  grain,  but  only  the  size, 
which  is  additional  reason  for  weakness. 

Benefits  of  Phosphorus. — Phosphorus  may  be  beneficial  on 
account  of  its  tendency  -to  eliminate  blow  holes,  thereby  promoting 
soundness.  It  decreases  shrinkage  ajso,  but  does  not  materially 
affect  the  hardness.  Its  most  distinctive  characteristic  is  its  power  Tr  A  x  M  F 
to  render  the  iron  more  fluid,  or  to  prolong  the  period  of  fluidity  XVIIL.  P-  458- 
to  such  an  extent  that  the  metal  has  opportunity  to  penetrate  to 
all  parts  of  the  mould,  thereby  producing  sharp  impressions. 
This  quality  commends  it  especially  as  a  constituent  of  irons  to 
be  used  in  making  castings  of  fine,  intricate  patterns  which  do  not 
require  much  strength.  In  castings  that  need  strength,  the  phos- 
phorus should  not  be  allowed  to  rise  much  above  }/2  per  cent. 
Where  fluidity  is  the  prime  requisite  I  per  cent,  or  even  more 
may  be  desirable. 

SULPHUR. 

In  general,  it  may  be  stated  that  from  a  metallurgical  stand- 
point sulphur  in  iron  presents  no  redeeming  features.  Therefore 
it  is  generally  allowed  to  be  present  only  in  quantities  which  are 
small  compared  to  those  of  other  elements.  Its  presence  is  vigor- 
ously, opposed  by  manganese,  and  also  by  the  furnace  conditions 
that  produce  high  silicon.  As  would  be  expected,  therefore,  it  is 
usually  low  in  high-silicon  irons.  High  sulphur  is  usually  an 
accompaniment  of  low-silicon,  because  the  low  temperature  of 
formation  permits  the  absorption  of  sulphur. 

Effect  of  Sulphur. — Since  silicon  is  usually  low,  high  sulphur 
is  generally  accompanied  by  much  combined  carbon,  and  therefore 
it  has  acquired  the  reputation  of  being  a  hardener  of  iron.   It  seems 
to  be  clearly  established  that  the  presence  of  sulphur  is  accompanied 
by  an  increase  in  hardness  and  shrinkage  of  castings,  together 
with  increased  density  and  liability  ta  crack.     Its  presence  may    Tr  A  T  M  E 
not  be  injurious  in  certain  classes  of  work,  but  for  castings  which    xxm->  P-  382- 
must  be  accurate  to  the  pattern,  or  must  be  machined,  sulphur 
should  not  rise  much  above  0.05  per  cent.     When  manganese  is 


30 


Blast  Furnace. 


present  in  quantity  above  y>  per  cent,  the  greater  part  of  the 
sulphur  is  found  combined  with  it  as  manganese  sulphide.  In 
this  condition  it  does  not  exert  its  usual  deleterious  effect  upon 
the  metal,  and  if  the  period  of  fluidity  is  sufficiently  long  this 
sulphide  will  float  up  to  the  surface  and  separate  itself  entirely 
from  the  metal. 

SUMMARY  OF   INFLUENCE  OF   METALLOIDS. 

The  effect  of  the  metalloids  upon  cast  iron  may  be  summarized 
as  in  the  following  table.  By  this  it  may  be  seen  that  the  effects  of 
manganese  and  sulphur  are  somewhat  similar,  while  those  of  sili- 
con and  phosphorus  are  opposed  to  them : 


Si. 

Total  0 Decreases. 

Graphite Increases. 

Comb.  C Decreases. 

Soundness Promotes. 

Strength Decreases. 

Shrinkage Decreases. 

Chill Decreases. 

Hardness Decreases. 

Fluidity Decreases. 

Sulphur Excludes. 


Mn. 

P. 

Increases. 

Decreases. 

Decreases. 

Neutral. 

Increases. 

Neutral. 

Promotes. 

Promotes. 

Decreases. 

Decreases. 

Increases. 

Neutral. 

Increases. 

Neutral. 

Increases. 

Neutral. 

Neutral. 

Increases. 

Excludes. 

Neutral. 

s. 

Neutral. 

Decreases. 

Increases. 

Neutral. 

Decreases 

Increases. 

Increases. 

Increases. 

Neutral. 


The  diagram  below  illustrates  graphically  the  opposing  effects 
of  silicon  and  manganese  upon  the  other  three  elements. 


Diagram  Illustrating  Effects  of  Silicon  and  Manganese. 


Introductory. 


31 


ALUMINUM. 

Aluminum  cannot  be  looked   upon  as   a  constituent  of  pig 
iron,  but  its  cheapness  has  made  it  available  of  late  years  as  a 
metallurgical  reagent.     It  may  be  added,  therefore,  whenever  the 
effects  which  it  produces  are  desired.     In  general  its  effects  re- 
semble closely  those  of  silicon.     It  changes  combined  carbon  to    T^A^I.  M 
graphite,  it  increases  strength  and  decreases  shrinkage,  chill  and 
fluidity.     Its  effect  is  most  marked  between  0.5  per  cent,  and  2 
per  cent     Above  2  per  cent,  there  is  a  decrease  of  total  carbon, 
and  above  5  per  cent,  its  power  to  form  graphite  is  practically 
gone.    It  never  decreases  the  combined  carbon  below  I  per  cent., 
which  indicates  that  its  effect  is  not  so  complete  as  that  of  silicon,    Ingt  Jour 
although  it  is  more  active  in  small  quantities.     Between  0.5  per   p902°44n-' 
cent,  and  4  per  cent.,  chilling  appears  impossible.     Its  influence  is 
well  shown  by  the  analyses  of  Melland  and  Waldron  in  the  fol- 
lowing table  : 

Si    ................  0.24  0.23  0.21  0.19  0.21  0.28  0.22  ......      0.26 

Al     ...............  0.00  0.02  0.16  0.25  0.53  1.78  3.82  4.24     8.31   11.80 

Total    C  ............  3.90  3.93  4.00  3.9G  3.83  4.07  3.59  3.57      3.32      3.12 

Graph,    (chilled)  ____  0.38  0.30  0.32  0.91  3.06  2.96  t.53  2.28     0.66     0.20 

Graph,    (sand)  ......  0.38  1.20  3.01  3.49  2.93  2.93  2.54  2.49     0.99     0.20 


OTHER    ELEMENTS. 

Occasionally  rarer  elements  are  found  in  pig  iron.  Almost  all 
ores  contain  traces  of  arsenic,  which  is  readily  reduced  and  enters 
the  iron.  It  forms  with  it  an  arsenide,  which  js  weak  and  brittle;  instjo 

1888,  I., 

therefore  its  presence  has  an  injurious  effect.    As  it  rarely  occurs   p-171- 
in  quantity  exceeding  0.04  per  cent.,  however,  the  effect  is  hardly 
noticeable. 

Titanium  is  reduced  with  difficulty  in  the  blast  furnace,  and 
rarely  occurs  in  pig  iron  in  quantity  exceeding  i  per  cent.  In 
small  quantities  it  appears  to  have  a  very  beneficial  effect.  It 
increases  the  density  of  the  metal,  giving  it  greater  tenacity  and  P 
resistance  to  wear.  When  chilled,  the  metal  resists  the  hardest 
steel  and  is  especially  good  for  car  wheels.  Wrought  iron  or 
steel  made  from  titaniferous  pig  are  unusually  strong  and  tough 
and  never  show  red-shortness  or  cold-shortness.  Whether  the 
beneficial  effect  is  due  to  the  small  traces  of  titanium  or  to 


iron  Age, 
"* 


32  Blast  Furnace. 

Trxxi!',  J!'832.'  the  freedom  from  phosphorus  and  sulphur,  which  is  the  peculiarity 
of  all  titaniferous  ores,  is  not  clearly  proven.  Iron  made  from 
titaniferous  ores  without  absorbing  any  titanium  appears  to  be 
superior  to  ordinary  irons. 

PHYSICAL  PROPERTIES  OF  CAST  IRON. 

The  effect  of  various  physical  conditions  upon  the  properties 
of  cast  iron  may  be  as  great  as  the  effects  of  variation  in  com- 
position itself.  The  two  are  so  inextricably  bound  together  that 
it  is  generally  impossible  to  say  where  one  ends  and  the  other 
begins. 

INFLUENCE  OF   HEAT   ON    CAST   IRON. 

Specific  Gravity. — The  matrix  of  cast  iron  tends  to  crystal- 
lize in  octahedra,  surrounding  flakes  of  graphite.  The  presence  of 
the  graphite  lowers  the  specific  gravity  of  the  metal  in  the  ratio 
of  2.2  to  7.8.  The  graphite  represents  12  to  15  per  cent,  by  bulk, 
and  as  a  result,  gray  cast  iron  usually  has  a  specific  gravity  of  about 
7.2.  The  specific  gravity  of  the  metel  is  greatly  affected  by  the 
condition  of  the  carbon  and  is  therefore  variable.  Iron  which  has 
a  specific  gravity  of  7.25  when  gray,  may  have  over  8  when 
chilled.  This  is  due  to  the  contraction  of  the  metal  during  cool- 
ing. Chilled  samples  generally  show  considerable  shrinkage  spaces 
in  the  top,  while  gray  iron,  on  the  other  hand,  when  made  to 
solidify  between  rigid  walls,  often  extrudes  some  metal  during 
solidification.  The  rate  of  cooling  also  affects  the  specific  gravity, 
so  that  small  sections  always  have  a  lower  specific  gravity  than 
large  ones  cast  from  the  same  metal.  The  specific  gravity  of  cast 
iron  when  molten  is  less  than  when  cold,  but  greater  than  when 

Iron  Age, 

Aug.  10, 1905,  foot.  Solid  gray  iron  when  thrown  into  a  bath  of  molten  iron 
will  sink  at  first,  but  when  heated  through  will  rise  and  float  until 
melted.  The  reason  for  these  phenomena  is  revealed  by  observa- 
tion of  the  curves  made  by  cast  iron  when  cooling. 

Expansion  and  Shrinkage — If  a  test  bar  be  cast  between  a 
fixed  surface  and  a  movable  contact  which  is  connected  to  a  re- 
cording device,  it  will  show  a  series  of  expansions  immediately 
after  becoming  solid.  Gray  iron  shows  three  distinct  expansions 


Introductory. 


33 


which  are  scarcely  distinguishable  in  white  iron.  Each  expan- 
sion probably  represents  a  period  of  molecular  rearrangement. 
The  third  expansion,  which  is  the  most  marked,  is  due  to  the  sepa- 
ration of  graphite  and  is  followed  by  regular  contraction  until 
the  iron  is  quite  cold.  The  net  shrinkage  of  the  casting  will  be 
the  algebraic  sum  of  these  expansions  and  contractions,  and  there- 
fore will  be  smaller  the  greater  the  expansion.  Since  the  expan- 
sion is  caused  by  the  separation  of  graphite,  it  follows  that  shrink- 
age will  be  decreased  by  any  condition  which  creates  graphite, 
such  as  the  presence  of  silicon,  large  cross  section,  slow  cooling, 
etc.  For  example,  a  cross  section  of  */2  inch  with  2^/2  per  cent, 
silicon  shows  no  more  expansion  than  a  2-inch  section  with  I  per 
cent,  silicon.  A  i-inch  section  will  show  a  maximum  expansion 
inside  of  20  minutes,  while  a  4-inch  section  needs  at  least  an 
hour.  Expansion  is  decreased  by  the  presence  of  sulphur,  but 
not  appreciably  affected  by  phosphorus  and  manganese.  The 
temperature  at  which  the  separation  of  graphite  occurs  has  been 
determined  to  be  between  1300  degrees  F.  and  1400  degrees  F. 
The  other  two  expansions,  when  present,  occur  at  about  1650 
degrees  F.  and  2000  degrees  F.  They  are  all  characterized  by  a 
retardation  in  the  rate  of  cooling,  which  Indicates  an  evolution 
of  heat  resulting  from  the  molecular  changes. 

Melting  Point  of  Cast  Iron. — Moldenke  has  found  that  the 
melting  points  of  pig  irons  range  from  close  to  2000  degrees  F. 
for  white  irons,  to  nearly  2300  degrees  F.  for  gray.  That  graphite 
recombines  with  iron  before  melting  is  proven  by  the  fact  that  gray 
iron  heated  to  whiteness  but  not  melted  shows  the  third  expansion 
on  cooling  again.  The  higher  melting  points  of  graphitic  irons 
are  due  to  the  delay  necessary  to  effect  this  recombination.  The 
variation  in  the  apparent  melting  points  is  not  strictly  in  propor- 
tion to  the  quantity  of  graphite  present,  because  the  temperature 
necessary  is  greatly  influenced  by  the  rate  of  reabsorption  of 
graphite* 

Pipes  and  Cavities. — When  molten   iron  is  poured  into  a 
mould,  the  surface  of  the  metal  which  is  in  contact  with  the  rela- 
tively cold  mould  solidifies  first  and  expands  during  the  first  few 
minutes  of  cooling.    By  the  time  it  starts  to  contract,  it  finds  itself 
f opposed   by   the   expansive   force   of   some    subsequently   cooled 


Inst.  Jour., 
1895,  I., 
p.  227. 


Iron  Age, 
May  24, 1906, 
p.  1671. 


Iron  T.  R., 
Oct.  27, 1898. 


34  Blast  F'nrnace. 

material.  As  a  result,  before  contraction  can  take  place,  the  en- 
veloping shell  of  metal  becomes  so  rigid  that  it  cannot  shrink 
to  accommodate  itself  to  the  contracting  interior,  and  unless  fresh 
molten  metal  is  supplied  by  means  of  "  risers  "  or  "  sinkheads," 
pipes  or  cavities  may  result. 

Rate  of  Cooling  — The  prolongation  of  fluidity  and  the  differ- 
ent rates  of  cooling  tend  to  foster  two  undesirable  conditions,  viz., 
segregation  and  internal  strains.  By  segregation  is  meant  the 
partial  concentration  of  one  or  more  of  the  metalloids  in  any 
portion  of  the  mass  of  metal.  Such  concentrations  must  occur 
before  solidification  and,  as  they  take  time,  are  naturally  more 
marked  in  the  centre  of  the  mass,  since  it  remains  fluid  longest. 
The  condition  is  fostered,  also,  by  the  presence  of  those  elements 
which  lower  the  melting  point  of  metallic  iron,  particularly  car- 
bon and  phosphorus.  Uniformity  of  composition  is  promoted  by 
shortening  the  period  of  fluidity  as  much  as  is  practicable.  Sud- 
den cooling,  on  the  other  hand,  sets  up  internal  strains,  which 
may  cause  more  damage  than  segregation.  It  is  not  uncommon 
for  castings  to  break  quite  unaided  on  Account  of  internal  strains. 
Such  a  condition  may  be  relieved  by  annealing,  that  is,  by  allow- 
ing the  mass  of  metal  to  cool  slowly  from  a  high  temperature, 
thereby  giving  time  for  molecular  adjustment  in  the  solid  condi- 
tion. The  annealing  temperature  should  be  uniform  and  well 
above  redness.  The  temperature  may  be  due  to  the  initial  heat 
of  the  casting,  or  to  a  subsequent  reheating.  Annealing  usually 
decreases  the  strength  of  cast  iron  by  changing  some  of  the 
combined  carbon  to  graphite,  but  it  usually  strengthens  a  casting 
through  permitting  the  adjustment  of  initial  internal  strains. 

Effect  of  Shock.— It  was  first  observed  by  Outerbridge  that 
TT.  A.  I.M.  E.,  an  effect  similar  to  annealing  could  be  produced  in  castings  by 
successive  shocks,  such  as  result  from  cleaning  them  in  a  tumble- 
barrel  or  tapping  with  a  hammer.  He  attributed  this  result  to 
the  mobility  of  molecules  of  iron  which  appear  able  to  readjust 
themselves  even  in  the  solid  state.  Keep  observed  that  similar 
treatment  also  makes  slight  changes  in  the  volume  and  strength 
of  castings. 

Effect  of  Repeated  Heatings — That  cast  iron  undergoes  a 
marked  change  in  volume  through  the  action  of  heat  was  proved 


Introductory.  35 

by  Outer-bridge.  Repeated  heatings  and  coolings  result  in  per- 
manent expansion,  at  times  causing  serious  buckling.  The  change 
in  volume  is  due  to  continuous  pushing  out  of  the  crystals,  which 
do  not  return  to  place  on  cooling,  but  leave  open  spaces.  The 
effect  is  most  active  at  1450  degrees  F.,  at  which  temperature 
33  treatments  are  required  to  exhaust  the  action.  A  bar  i  inch 
square  and  about  15  inches  long  gained  12  per  cent,  in  length  and 
14  per  cent,  in  thickness,  giving  a  total  increase  in  volume  of 
more  than  40  per  cent.  The  specific  gravity  fell  below  5,  and 
the  strength  to  about  one-third  of  that  which  it  originally  pos- 
sessed. 

STRENGTH  OF  CAST  IRON. 

When  pig  iron  is  to  be  converted  into  steel  or  wrought  iron, 
the  knowledge  of  its  physical  properties  is  of  little  value.  It  is 
important  only  that  the  composition  of  the  pig  should  be  ap- 
propriate to  the  method  of  conversion.  If,  however,  the  iron  is 
to  be  used  as  a  material  of  construction,  in  the  form  of  castings, 
its  physical  properties  are  of  vital  importance.  The  property 
which  naturally  demands  first  consideration  is  strength,  in  as  much 
as  a  weak  metal  would  be  of  comparatively  little  use  in  structures. 
Of  scarcely  less  importance,  however,  is  hardness,  or,  more 
properly,  softness,  since  on  account  of  their  natural  roughness 
most  castings  need  to  be  smoothed  or  shaped  in  places  in  order 
to  make  accurate  contacts.  Excessive  hardness,  therefore,  should 
be  avoided  when  much  machining  is  necessary. 

TESTING    CAST    IRON. 

The  most  usual  tests  for  determining  the  strength  of  cast  iron 
are  tensile,  compressive  and  transverse. 

Tensile  Strength — The  tensile  tests  are  made,  by  pulling  a 
test  bar  of  carefully  measured  cross-section  until  it  breaks.  The 
strength  needed  to  produce  rupture  is  known  as  the  ultimate 
tensile  strength  and  is  usually  expressed  in  pounds  per  square 
inch  of  cross-section.  The  tensile  strength  of  cast  iron  is  low  as 
compared  to, that  of  wrought  iron  and  steel,  hence  it  is  almost 
never  used  for  tensile  purposes.  This  test  is,  therefore,  of  little 


36  Blast  Furnace. 

importance    commercially,    although    it    furnishes    a    comparative 
guide  to  mechanical  properties. 

Compressive  Strength. — Compressive  tests  are  usually  per- 
formed by  submitting  small  cubes  of  the  metal  to  a  crushing  force 
until  rupture  takes  place.  The  results  are  usually  expressed  in 
pounds  per  square  inch  of  cross-section  of  the  metal.  The  re- 
sistance to  compression  of  cast  iron  is  so  high  that  tests  are  usually 
considered  unnecessary. 

Transverse  Strength — Transverse  strength  tests  are  applied 
to  the  middle  of  a  test  bar  which  is  supported  at  the  ends.  They 
are  of  two  kinds,  known  respectively  as  "  dead-load  "  and  "  im- 
pact "  tests.  A  dead  load  test  is  a  static  test,  applied  by  quietly 
increasing  the  gravitational  force  on  the  bar  without  sudden 
shocks.  The  impact  test  is  a  dynamic  test  applied  by  means  of 
the  momentum  of  a  known  weight  falling  from  a  known  height 
under  the  force  of  gravity.  The  results  in  each  case  are  usually 
expressed  in  terms  of  pounds  per  square  inch  of  cross-section  of 
the  test  bar.  Transverse  tests  are  the  most  important,  hence  the 
most  usual. 

Testing  Terms.  — The  amount  of  force  applied  in  making 
strength  tests  is  usually  known  as  the  stress.  The  effects  of  the 
stress  upon  the  test  piece  are  called  strain.  The  amount  which  a 
given  stress  on  a  straight  bar  will  make  it  deviate  from  a  straight 
line  is  called  deflection,  and  is  measured  usually  in  fractions  of  an 
inch.  If  the  deflection  is  completely  obliterated  on  the  removal  of 
the  stress,  the  bar  is  said-to  be  perfectly  elastic.  Most  metals 
are  perfectly  elastic  up  to  a  certain  limiting  stress  where  elasticity 
ceases.  This  stress  is  the  measure  of  the  elastic  limit  of  the 
metal.  When  a  stress  in  excess  of  the  elastic  limit  of  a  metal  is  ap- 
plied and  removed,  the  metal  does  not  conform  to  its  original  shape 
but  retains  a  greater  or  less  deflection,  which  is  known  as  per- 
manent set.  This  is  measured  in  the  same  way  as  deflection.  A 
body  which  shows  no  deflection  under  stress  is  said  to  possess 
perfect  rigidity. 

Testing  Conditions. — Since  cast  iron  is  subject  to  such  wide 

Keep's    variation   in   composition,   and   its  properties   are   so  profoundly 

cast  iron."    a^ectecj  b    attendant  circumstances,  it  follows  that  in  order  that 


Introductory.  37 

tests  may  be  reasonably  comparable,  the  test  bars  should  be  made 
similar  in  all  respects.  The  following  are  some  of  the  causes  of 
errors:  Different  sized  test  bars  cool  at  different  rates  and  there- 
fore the  larger  the  test  bar  the  weaker  it  will  be  per  unit  of  cross- 
section.  Square  bars  show  greater  strength  for  the  same  cross- 
section  than  round  ones.  Bars  cast  horizontally  are  stronger  than 
those  cast  vertically,  and  those  cast  in  green  sand  show  more 
strength  than  those  cast  in  dry  sand.  Bars  from  a  large  casting 
will  appear  stronger  than  those  from  a  small  one.  The  centre  of  a 
casting  is  always  weaker  than  the  outside.  Low  silicon  gives 
strong  large  castings  and  weak  small  ones,  while  high  silicon  gives 
strong  small  castings  and  weak  large  ones. 

The  standard  test  bar  for  cast  iron  is  15  inches  long  by  1*4 
inches  square,  moulded  in  damp  sand,  from  which  the  pattern  is 
withdrawn  without  tapping.  The  bars  are  cleaned  by  brushing 
only,  and  the  load  applied  gradually  midway  between  supports, 
12  inches  apart. 


CHAPTER  I. 

MATERIALS  OF  MANUFACTURE. 

As  pointed  out  .in  the  introductory  chapter,  cast  iron  in  the 
form  of  pig  iron  is  practically  the  only  ferrous  product  that  is 
now  produced  direct  from  iron  ores.  The  operation  is  carried  out 
in  a  tall,  cylindrical  furnace,  known  as  a  "  blast  furnace,"  into 
the  top  of  which  the  raw  materials  are  charged,  and  from  the 
bottom  of  which  the  iron  is  drawn  in  the  molten  state. 

The  materials  which  go  to  make  up  the  charge  of  a  blast 
furnace  fall  naturally  under  three  heads ;  namely,  ores,  fuels  and 
fluxes. 

The  ores  comprise  the  iron-bearing  portion  of  the  charge. 
The  iron  may  be  present  in  the  ore  in  any  of  its  many  compounds, 
providing  that  the  ore  is  rich  enough  to  pay  for  the  treatment. 
The  compounds  most  usually  treated  are  oxides. 

The  fuels  are  necessary  in  order  to  furnish  the  heat  needed  to 
carry  on  the  reactions  which  take  place  in  the  furnace,  and  to 
melt  the  resulting  products.  They  furnish,  also,  the  reagent  for 
removing  the  oxygen  from  combination  with  the  iron. 

The'  duty  of  the  fluxes  is  "to  make  fluid  the  infusible  earths 
which  accompany  the  charge,  by  uniting  with  them  to  form  com- 
binations that  may  be  readily  melted  and  drained  from  the  furnace 

ORES  OF  IRON. 

An  ore  of  iron  consists  primarily  of  two  constituents ;  viz.,  a 
compound  of  iron  mixed  with  a  gangue  of  earthy  materials.  It 
may  be  compared,  for  purposes  of  illustration,  to  a  mixture  of 
iron-rust  and  dirt.  The  problem  of  the  smelter  is  the  extraction 
of  the  iron  from  its  combination,  and  the  fluxing  of  the  earthy 
constituents.  When  these  reactions  take  place  at  sufficiently  high 
temperatures,  we  have,  as  products  of  the  operation:  (i)  the 
molten  metal  which  has  been  separated  from  its  combination  and 
melted,  and  (2)  a  liquid  slag,  which  is  a  new  compound  formed 


40  Blast  Furnace.  . 

by  uniting  the  flux  with  the  earthy  materials  which  constituted 
the  gangue.  These  two  products  have  very  different  specific 
weights,  and  if  allowed  to  lie  quietly,  separate  into  two  layers ; 
the  lower,  pig  iron,  the  upper,  slag.  By  means  of  tapping-holes 
at  different  levels,  they  may  be  drawn  off  separately. 

CONSTITUTION    OF   IRON    ORES. 

The  compounds  of  iron  best  suited  to  smelting  in  a  blast  fur- 
nace are  the  oxides,  although  carbonates  and  silicates  are  some- 
times used.  Oxides  of  iron  are  compounds  of  iron  and  oxygen 
which  have  the  formulas  Fe2O3  and  Fe3O4,  and  contain  re- 
spectively 70  per  cent.  Fe  and  72.4  per  cent.  Fe.  The  carbonate 
has  the  formula  FeCCX  and  contains  48.3  per  cent.  Fe.  The 
silicate  may  be  represented  by  the  formula  FeSiCX,  which  contains 
42.4  per  cent.  Fe.  It  is  evident,  then,  that  from  the  point  of  rich- 
ness, oxides  are  far  superior  to  carbonates  and  silicates.  More- 
over, the  oxides  yield  metallic  iron  upon  the  simple  removal  of 
the  oxygen,  whereas  in  the  cases  of  carbonates  and  silicates,  CCX, 
and  SiO2  remain  to  be  dealt  with. 

Inii.Ji896,'  The  gangue  material  of  iron  ores  usually  consists  mainly  of 
silica,  with  varying  proportion  of  alumina.  There  are  usually 
present,  also,  various  bases,  such  as  lime,  magnesia  and  oxides  of 
manganese  and  the  alkalis,  which  may  or  may  not  exist  com- 
bined with  the  silica  and  alumina.  These  combinations  of  siliceous 
and  basic  substances  may  be  in  such  proportions  that  they  are 
self-fluxing,  and  hence  require  no  added  flux.  Usually,  however, 
there  is  a  deficiency  of  bases,  and  at  least  part  of  the  acid  con- 
stituents,— silica,  alumina,  and  sulphur, — must  be  supplied  with 
them. 

NOMENCLATURE  OF  IRON   ORES. 

The  various  ores  of  iron  are  designated  by  names  which  are 
more  or  less  descriptive  of  prominent  characteristics. 

Magnetite. — Magnetite,  Fe3O4,  containing  72.4  per  cent.  Fe 
when  pure,  is  so  called  because  it  is  so  strongly  magnetic  that  it  can 
be  picked  up  by  a  magnet  almost  as  readily  as  metallic  iron  itself. 
It  is  very  heavy,  having  a  specific  gravity  of  5.2,  is  generally  very 
hard,  is  steel-gray  in  color,  and  gives  a  black  streak  when  rubbed  on 


Materials  of  Manufacture.  41 

unglazed  porcelain.     It  occurs  frequently  as  octahedral  crystals.  j 
One  molecule  is  sometimes  replaced  by  Mn.,  which  would  seem  to  p 
indicate  that  its  constitution  is  FeFe2O4,  a  ferrous  ferrate.     It 
has  the  same  composition  as  the  black  scale  which  forms  on  iron 
at  temperatures  above  redness,  as  rolling-mill  scale.     Such  scale 
is  the  result  of  the  action  of  the  oxygen  of  the  air  upon  the  iron  at 
high  temperatures. 

Hematite. — Hematite,  or  Red  Hematite,  Fe2O3,  containing 
70  per  cent,  of  Fe  when  pure,  has  a  deep  red  color  and  derives  its 
name  from  the  Greek  word  "  haima,"  meaning  blood.  It  gives  a 
red  streak  to  unglazed  porcelain,  and  is  only  slightly  affected  by 
a  magnet.  It  occurs  frequently  in  columnar  formation,  resembling 
bundles  of  fibres,  and  also  in  a  brilliant  scaly  structure,  when  it  is 
called  specular  hematite.  Generally,  however,  it  is  granular  or 
massive,  sometimes  botryoidal  or  stalactitic,  and  often  unctuous  to 
the  touch.  It  crystallizes  in  the  rhombohedral  system,  and  has 
hardness  and  specific  gravity  about  equal  to  that  of  magnetite.  A 
familiar  form  is  the  red  scale  which  appears  on  cold  finished 
steel,  or  the  deep  red  rust  which  attacks  iron  or  steel  in  dry  atmos- 
pheres. It  is  identical  in  composition  with  common  red  iron-rust. 

Limonite. — Limonite,  2Fe2O33H2O  is  a  hydrous  hematite, 
containing  59.9  per  cent,  metallic  iron  and  14.5  per  cent.  H2O  of 
combination.  It  gives  a  yellow  streak  on  unglazed  porcelain,  and 
hence  is  sometimes  said  to  'derive  its  name  from  the  French 
"  limon,"  meaning  lemon.  As  it  is  found  largely  in  bogs  or  mead- 
ows, it  is  more  probable  that  the  name  is  derived  from  the  Greek 
"  leimon,"  meaning  meadow.  It  occurs  usually  in  massive  form, 
showing  frequent  botryoidal,  concretionary  or  mamillary  forma- 
tions. It  is  somewhat  softer  than  hematite,  and  its  specific  gravity 
falls  below  4.  It  differs  from  red  hematite  only  in  the  fact  that  it 
contains  water,  and  may  therefore  be  considered  a  hydrous  hema- 
tite. This  water  is  not  simply,  moisture  that  can  be  evaporated  at 
212  degrees  F.,  but  is  water  of  combination  which  can  be  driven 
off  only  at  higher  temperatures.  Its  elimination  destroys  the 
variety,  however,  and  leaves  the  red  hematite  as  the  result  of  the 
dehydration. 

A  considerable   number   of   hydrous   hematites,    representing 


42  Blast  Furmicc 

various  degrees  of  1ml ration,  stand  between  hematite  and  limon- 
ite.  They  are  of  yellowish  brown  color,  and  give  streaks  varying 
between  the  red  of  hematite  and  the  yellow  of  limonite.  They 
are  generally  known  as  Brown  Hematites.  A  familiar  form  of 
limonite  is  the  fresh  yellow  rust  of  newly-rusted  iron,  before  it 
has  turned  to  the  characteristic  deep  red  color  of  maturity. 

Siderite. —  Siderite,  FeCO3,  contains  48.3  per  cent.  Fe  and 
41.4  per  cent.  CO2.  It  is  frequently  known  as  Spathic  Ore  from 
the  resemblance  of  its  cleavage  to  that  of  feldspar.  It  crystallizes 
in  the  rhombohedral  system,  is  softer  than  the  oxides,  of  lower 
specific  gravity,  and  does  not  give  a  characteristic  colored  streak. 
It  changes  to  limonite  and  hematite  on  weathering.  It  is  rarely 
used  as  an  ore  in  its  raw  state,  but  generally  is  subjected  to  a  pre- 
liminary calcination  to  remove  the  CCX.  This  leaves  behind  only 
the  iron  and  oxygen  in  the  familiar  form  of  hematite. 

Silicates — Silicates  of  Iron  rarely  occur  in  nature  in  quan- 
tity or  richness  sufficient  to  warrant  their  use  as  ores,  but  in 
the  form  of  cinder  from  heating  and  puddling  furnaces  and  slags 
from  steel-melting  or  other  refining  furnaces,  they  frequently  find 
their  way  into  the  blast  furnace.  Such  materials  rarely  carry  more 
than  55  per  cent,  of  iron,  and  generally  have  20  to  30  per  cent. 
SiO2  to  be  fluxed.  They  are  therefore  productive  of  much  slag 
and  may  be  advantageously  mixed  with  rich  ores  which  have  a 
deficiency  of  slag-making  ingredients. 

Other  Elements  in  Iron  Ores. — Other  elements  occur  in  iron 
ores  which  have  the  most  potent  influence  upon  their  value. 
Chief  of  these  are  phosphorus  and  sulphur. 

Phosphorus  is  usually  present  in  ores  of  irpn  in  the  form  of 
a  phosphate  of  calcium  called  apatite,  which  has  the  formula 
Ca3P2Os.  Apatite  frequently  appears  in  the  form  of  hexagonal 
prisms,  having  pyramidal  ends. .  It  has  a  vitreous  to  sub-resinous 
lustre,  and  generally  a  pale  brown  color,  but  may  be  green,  blue, 
yellow,  red  or  white.  It  frequently  contains  chlorine  and  fluorine. 

Sulphur  usually  occurs  in  the  form  of  pyrite  or  marcasite, 
both  sulphides  of  iron,  having  the  formula  FeS2..  They  are 
usually  of  a  pale  yellow  color  and  a  brassy  lustre,  and  are  gen- 


Materials  of  Manufacture.  43 

erally  crystallized,  with  striated  faces.     The  sulphur  in  the  great 
Cornwall,  Pa.,  deposit  occurs  as  a  cupriferous  pyrite. 

Oxide  of  Manganese  also  occurs  frequently  as  black  layers 
or  lumps  scattered  through  ores  of  iron,  particularly  in  the  South- 
ern States. 

PHYSICAL   CONDITION   OF  ORES. 

The  physical  conditions  of  iron  ores  show  quite  as  wide  varia- 
tion as  the  chemical  compositions.  Not  only  does  the  product  of 
almost  every  mine  present  distinct,  characteristic  features,  but 
different  parts  of  the  same  mine  may  yield  ore  of  quite  different 
quality  and  properties.  The  occurrence  of  ore  ranges  from  soft 
beds  of  finely  divided  oxides  that  can  be  scooped  up  by  steam 
shovels,  to  hard,  flint-like  deposits,  that  must  be  attacked  with  a 
diamond  drill.  As  we  shall  see  later,  neither  of  these  extremes 
is  desirable.  The  very  hard  deposits  are  expensive  to  mine,  and 
the  run  of  mine  product  is  so  coarse  that  it  has  to  be  crushed 
before  charging  in  the  furnace,  which  adds  to  the  expense.  When 
crushed,  however,  these  ores  are  most  desirable,  as  they  give  an 
open  charge  and  small  loss  in  flue-dust.  Fine  ore,  while  easy  to 
mine  and  handle,  tends  to  cause  irregularities  in  the  operation  of 
the  furnace,  and  much  of  it  is  carried  off  by  the  gases.  The  mag- 
netites of  New  York  and  New  Jersey  are  of  good  physical  condi- 
tion, but  they  are  so  dense  that  it  is  said  they  cannot  be  used  alone 
in  the  making  of  certain  grades  of  iron  without  excessive  con- 
sumption of  fuel.  The  ideal  ore  is  a  lumpy  ore  that  is  not  so 
dense  but  that  it  can  be  readily  permeated  by  the  furnace  gases. 

VALUATION    OF   ORES. 

The  value  of  an  ore  of  iron  depends  upon  many  conditions. 
Three  conditions*  at  least  may  be  considered  essential,  the  ab- 
sence of  any  one  of  which  may  prove  fatal  to  an  ore  otherwise 
desirable.  These  three  requirements  are:  richness,  accessible 
location,  and  suitable  composition. 

Richness.  — By  the  richness  of  an  ore  is  meant  the  percentage 
of  metallic  iron  it  contains.  The  word  "  unit  "  is  generally  used  to 
represent  a  per  cent,  of  iron.  An  ore  containing  60  per  cent,  of 
metallic  iron  is  therefore  said  to  contain  60  units.  Since  the 


44  Blast  Furnace. 

metallic  content  of  the  ore  is  the  only  part  that  has  a  market 
value,  it  is  clear  that  its  proportion  is  of  vital  importance,  since 
it  must  stand  not  only  the  costs  of  its  own  extraction,  but  also 
the  additional  fixed  charges  of  mining  and  transportation.  Other 
things  being  equal,  however,  the  value  of  an  ore  does  not  advance 
at  the  same  rate  as  the  percentage  of  iron,  but  at  a  more  rapid 
rate.  This  is  because  every  additional  pound  of  oxide  of  iron 
per  ton  of  ore  means  one  pound  less  of  gangue  to  be  fluxed, 
melted  and  handled.  The  price  of  ore  increases  therefore  at 
arbitrary  intervals.  For  example,  if  an  ore  ranging  from  50  to 
55  units  is  worth  6  cents  per  unit,  one  ranging  from  55  to  60 
units  may  be  7  cents,  and  60  to  65  units,  8  cents  per  unit. 

Location — A  rich  ore  may  be  valueless  if  its  geographical 
location  is  remote  or  inaccessible.  Under  this  head  there  are  two 
fixed  items  to  be  considered  in  estimating  the  value  of  ores ;  name- 
ly, the  cost  of  mining  and  the  cost  of  transportation.  A  deposit 
of  rich  ore  may  be  within  the  usual  radius  of  transportation,  yet 
its  nature  be  such  that  the  cost  of  mining  is  so  high,  compared 
with  more  tractable  deposits,  that  it  fails  to  prove  a  profitable 
undertaking.  On  the  other  hand,  many  rich  and  workable  de- 
posits in  the  West  are  so  far  from  the  centres  of  iron  smelting  that 
they  will  not  be  available  until  the  more  accessible  supplies  are 
exhausted,  or  until  a  demand  is  developed  which  permits  of  local 
consumption. 

Composition.  — It  may  happen  that  an  ore,  both  rich  and  ac- 
cessible, contains  components  which,  on  account  of  their  injurious 
effects  on  pig  iron,  make  it  practically  worthless.  Since,  however, 
not  all  of  the  non-ferrous  components  are  harmful,  it  is  necessary 
to  know  the  nature  and  quantity  of  each  before  deciding  the  value 
of  the  ore. 

The  non-ferrous  elements  may  for  the  moment  be  divided  into 
three  classes,  according  to  their  behavior  toward  the  iron  during 
smelting,  namely,  (i)  those  that  never  enter  the  iron,  (2)  those 
that  partially  enter  the  iron,  (3)  those  that  always  enter  the  iron. 

In  the  first  class  are  the  oxides  of  aluminum,  calcium,  mag- 
nesium and  the  alkalis.  They  may  be  dismissed  as  having  no  bear- 
ing on  the  ore  value  from  this  standpoint. 

Under  the  second  class  come  those  elements  which  may  enter 


Materials  of  Manufacture.  45 

the  iron  in  quantities  which  vary  as  the  furnace  is  operated,  and 
which  are  therefore  more  or  less  under  the  control  of  the  fur- 
naceman,  such  as  silicon,  sulphur,  and  manganese. 

The  case  of  silicon  is  quickly  disposed  of.  Since  very  little 
of  the  silicon  in  the  iron  is  derived  from  the  silica  in  the  gangue 
materials,  its  presence  does  no  harm  beyond 'decreasing  the  rich- 
ness of  the  ore. 

The  question  of  sulphur,  however,  is  more  serious.  Ores  which 
have  been  derived  from  the  oxidation  of  pyritous  deposits  contain 
considerable  quantities  of  residual  sulphur.  In  thoroughly  oxi- 
dized ores,  the  sulphur  that  may  once  have  existed  is  diminished 
to  a  mere  trace.  A  secondary  impregnation  of  sulphides,  however, 
may  introduce  a  considerable  quantity  of  sulphur  into  otherwise 
desirable  ore.  By  proper  furnace  manipulation  an  ore  running 
from  y2  to  i  per  cent,  sulphur  may  be  used  for  making  some  grades 
of  iron  which  are  fairly  low  in  sulphur.  If  sulphur  exists  in  the 
ore  in  greater  quantities,  it  is  advisable  to  remove  some  of  it  by  a 
preliminary  operation  of  roasting.  This  operation,  however,  adds 
to  the  expense,  and  its  cost  must  be  known  before  the  availability 
of  the  ore  can  be  determined.  The  presence  of  even  moderate 
quantities  of  sulphur  demands  additional  flux  and  fuel  for  its 
removal,  and  hence  its  presence  always  lessens  the  value  of  ore. 

Manganese,  being  somewhat  more  difficult  to  reduce  from  its 
oxides  than  iron,  is  never  fully  extracted  from  manganiferous 
ore.  The  quantity  extracted  is  affected  by  the  temperature  and 
other  conditions  of  the  furnace  hearth.  Under  ordinary  condi- 
tions the  extraction  ranges  from  50  to  75  per  cent,  of  the  manga- 
nese present.  As  we  have  seen,  manganese  in  quantity  ranging 
from  i  to  2  per  cent,  does  not  materially  injure  any  grade  of  pig 
iron,  and  is  a  positive  benefit  to  some  grades.  Therefore  it  is 
evident  that  manganese  in  an  ore  up  to  2  per  cent,  of  the  iron 
present  would  not  be  a  serious  defect.  If  the  percentage  rose  to 
5  or  10,  however,  the  ore  could  be  used  only  as  a  fraction  of  a 
mixture  with  non-manganiferous  ores.  If  the  manganese  rose  to 
or  above  15  or  20  per  cent,  of  the  iron  present  the  ore  would 
acquire  a  new  value,  as  it  would  then  be  available  for  the  produc- 
tion of  such  special  products  as  spiegeleisen  or  ferromanganese 


46  Blast  Funidcc. 

and1  would  no  longer  be  considered  as  available  for  the  production 
of  pig  iron. 

In  the  third  class  is  the  single  element  phosphorus.  Of  all 
the  non-ferrous  components  of  ore,  phosphorus  is  most  liable  to 
affect  its  value.  Its  presence  is  the  basis  of  the  great  division  of 
iron  ores  into  Bessemer  and  non-Bessemer  ores.  It  may  be  said 
briefly  that  this  classification  rests  on  the  facts  that,  (i)  practi- 
cally all  of  the  phosphorus  present  in  the  furnace  enters  the  pig 
iron;  (2)  in  the  Bessemer  process  of  making  steel  none  of  the 
phosphorus  so  accumulated  can  be  eliminated;  (3)  Bessemer  steel 
must  contain  less  than  o.i  per  cent,  phosphorus.  Therefore,  since 
all  of  the  phosphorus  in  the  ore  enters  the  iron  and  remains  in  the 
steel,  it  follows  that  an  ore  to  be  used  for  making  iron  for  the 
Bessemer  process  must  not  contain  more  phosphorus  than  will 
make  o.i  per  cent,  of  the  resulting  steel.  This  amount  approxi- 
mates */i000  part  of  the  iron  in  the  ore. 

The  classification  of  ores  as  Bessemer  and  non-Bessemer  was 
for  many  years  the  only  distinction  based  on  the  content  of  phos- 
phorus. With  the  development  of  other  processes  for  making  steel 
there  have  grown  up  other  distinctions  in  pig  iron,  which  have 
their  origins  in  the  phosphorus  content  of  the  ores. 

We  may  distinguish  five  types  of  pig  iron  whose  uses  are  de- 
termined primarily  by  their  content  of  phosphorus. 

(1)  Phosphorus  below  0.03  per  cent.,  known  as    low-phos- 
phorus pig,  and  used  chiefly  in  making  steel  castings  and  low- 
phosphorus  muck  bar  for  crucible  steel  melting.     It  requires  that 
the  ores  used  should  not  average  much  over  o.oi  per  cent,  phos- 
phorus, and  that  only  very  low  phosphorus  coke  and  limestone 
should  accompany  them. 

(2)  Phosphorus  below  o.i  per  cent,  or  Bessemer  pig,  to  be 
used  in  making  rolled  steel  by  the  Bessemer  or  acid  open  hearth 
process.     It  requires  that  the  ores  used  should  not  average  over 
0.05  per  cent,  phosphorus  with  average  coke  and  limestone. 

(3)  Phosphorus  below  0.2  per  cent.,  malleable  pig,  to  be  used 
in  making  malleable  iron  castings.     It  requires  that  the  ores  used 
should  not  average  over  o.i  per  cent,  phosphorus  with  average 
coke  and  limestone. 

(4)  Phosphorus  below  i  per  cent.,  foundry  and  basic  pig,  the 


Materials  of  'Manufacture.  47 

former  for  use  in  making  iron  castings,  the  latter  for  making 
steel  by  the  basic  open  hearth  process.  They  require  that  the  ores 
used  should  not  average  over  0.5  per  cent,  phosphorus  with 
average  coke  and  limestone. 

(5)  Two  to  3  per  cent,  phosphorus,  known  as  basic-Bessemer 
or  Thomas-Qilchrist  pig,  to  be  used  for  making  steel  by  the 
basic-Bessemer  or  Thomas-Gilchrist  process.  It  requires  that  the 
ores  should  not  average  less  than  i  to  1.5  per  cent,  phosphorus 
with  average  coke  and  limestone. 

RELATIVE  VALUE   OF  ORES. 

The  relative  values  of  ores  of  differing  compositions  depend 
upon  the  value  of  fuel  and  flux  needed  to  smelt  them.  Pig  iron  of 
a  given  composition  always  requires  a  constant  quantity  of  metal- 
lic iron,  whether  that  iron  is  extracted  from  a  rich  or  a  lean  ore. 
A  pig  containing  95  per  cent,  metallic  iron  must  always  have  95 
pounds  of  iron  in  each  hundred  of  pig.  If  the  ore  chances  to  be 
lean,  more  of  it  must  be  used.  Disregarding  the  gangue  for  the 
moment,  the  cost  of  extracting  95  pounds  of  metallic  iron  evi- 
dently consists  only  of  the  value  of  the  carbon  needed  to  reduce 
and  melt  it.  It  is  evident,  then,  that  for  a  given  fuel  this  cost 
must  be  constant  for  each  ton  of  pig,  no  matter  whether  the  ore 
be  rich  or  poor.  Therefore  the  relative  values  of  ores  are  not 
affected  by  the  cost  of  extracting  their  iron  content,  but  center 
entirely  in  the  relative  expense  of  treating  the  gangues.  The 
estimation  of  the  cost  of  treating  the  gangue  of  an  ore  naturally 
divides  itself  into  three  steps : 

(1)  Determining  the  amount  of  flux  needed  to  form  the  slag. 

(2)  Determining  the  amount  of  slag  formed. 

(3)  Determining  the  amount  of  fuel  needed  to  melt  the  slag. 
It  is  necessary  to  have  analyses  of  materials  before  such  an 

estimate  can  be  attempted.     Let  us  assume,  for  example,  an  ore 
to  have  the  following  composition  in  the  natural  state : 

Per  cent.  cent. 

Fe    42. SO         Si2O    16.1 4 

Mn    0.04  A12O3     2.SO 

P    0.13  CaO    0.07 

S    '. 0.04  MgO    0.53 

Combined   H,,O 12.84 

It  is  desired  to  ascertain  its  value  to  the  smelter  when  coke 


Tr.  A.  I.  M.  E., 

1892. 


48  Blast  Furnace. 

costs  $3  per  net  ton  and  limestone  $0.60  per  gross  ton  at  the 
furnace,  and  $2.30  represents  all  other  expenses  except  the  cost  of 
the  ore  and  $12  is  to  be  the  maximum  cost  of  the  pig  iron.  It  is 
required,  also,  that  the  pig  iron  should  contain  95  per  cent.  Fe 
and  i  per  cent.  Si.  Let  us  assume  that  it  has  been  found  by  ex- 
perience that  results  are  attained  best  when  the  ratio  of  bases  to 
acids  in  the  slag  is  1:1.2.  Moreover,  the  limestone  at  hand  con- 
tains 57  per  cent,  of  slag-forming  materials,  of  which  50  per  cent, 
is  available  base  -and  represents  its  efficiency.  The  fuel  affords 
78  per  cent,  available  carbon  and  requires  25  per  cent,  of  limestone 
to  flux  its  ash. 

As  pointed  out  by  Gordon,  the  heat  developed  in  the  average 
furnace  hearth  compared  with  the  heat  requirements  shows  that 
the  reduction,  impregnation  and  melting  of  pig  iron  usually  re- 
quires 66  per  cent,  of  carbon  for  its  accomplishment.  It  is  ob- 
served also  that  each  pound  of  slag  needs  about  a  quarter  of  a 
pound  of  carbon  to  melt  it. 

In  estimating  the  fuel  needed  by  the  above  ore  to  produce  a 
ton  of  pig  iron  with  blast  1000  to  1200  degrees  F.,  we  can  allow 
0.66  tons  of  carbon  for  the  iron  in  each  ton  of  pig  containing 
about  i  per  cent.  Si.  For  each  extra  pound  of  silicon  5  pounds 
additional  carbon  is  necessary.  In  estimating  the  cost  of  fluxing 
and  melting  the  gangue  the  first  step  is  to  determine  the  quantity 
of  stone  needed. 

The  balance  sheet  of  the  gangue  is  as  follows 

Acids.  Bases. 

SiO2    16.14  MnO     0.02 

A12OS     2.80  CaO     0.08 

MgO    0.53 

Total  acids 18.94 

SIO2  reduced  to  Si 0.01  Total  bases. 0.63 

Acids  to  be  fluxed 18.03  bases 

1.2    ratio  — - —  in  slag. 

acids 
3606 
1803 


Bases    needed 21 .63 

liases    present 0.63 


Bases  to  be  supplied 21.00 

21.00  •*-  0.50  (efficiency  of  stone)   —  42  per  cent,  of  stone. 
95 

—  :=  2.22  gross  tons  of  ore  needed  to  make  1  ton  of  pig. 
42.8 

2.22  X  0.42  —  0.9325  gross  ton  of  stone  needed  to  flux  the  gangue  of  2.22  tons  of 
the  ore. 


Materials  of  Manufacture.  49 

Having  found  the  quantity  of  stone  needed,  the  next  step  is  to 
find  the  weight  of  slag  made  by  the  ore.  This  amount  will  evi- 
dently be  the  sum  of  all  the  slag-forming  ingredients  in  the  gangue 
and  the  stone  used  to  flux  it,  thus : 

Gross  tons. 

Slag  from  the  ganguo  (18.03  +  0.6:5)  2.22  =: 0.4142 

Slag  from  the  stone,  0.9325  X  0.57  — 0.5315 


0.9457 

The  carbon  needed  to  melt  the  slag,  0.9457  X  0.25  = 0.2364 

The  carbon  needed  to  reduce,  impregnate  and  melt  the  iron  = 0.6600 


0.8964 
0.8964 

Of  coke  having  78  per  cent,  available  carbon  there  will  be  needed =  1.15 

0.78 
gross  tons,  or  2,575  pounds,  per  gross  ton  of  pig. 

The  fuel  needs  25  per  cent,  stone  to  flux  its  ash,  hence  the  total 
stone  needed  will  be  found  thus: 

Gross  tons. 

Stone  required  by  the  gangue  of  the  ore  ~ 0.9325 

Stone  required  by  fuel,  1.15  X  0.25  = , .  .    0.2875 


1.2200 

Allowing  5  per  cent,  loss  of  fuel  as  braize,  2575  pounds  in 
the  furnace  represents  2700  pounds  purchased  at  $3  per  net  ton, 
hence : 

The  fuel  per  ton  of  pig  iron  will  cost $4.05 

1.22  gross  tons  stone,  at  60  cents  per  ton 0.73 

Tne  fixed  charge,  salaries,  wages,  supplies,  repairs,  &c 2.30 


Total  cost  of  pig  iron,  exclusive  of  ore $7.08 

Total  cost  of  pig  iron  allowable $12.00 

Total  cost  of  pig  iron,  exclusive  of  ore 7.08 

Value  of  2.22  gross  tons  of  ore $4.92 

or  $2.20  per  gross  ton,  delivered. 

Such  an  ore  could  be  valued  at  5  cents  per  unit  on  a  basis 
of  43  per  cent.  Fe.  A  premium  of  7^  cents  per  unit  above  43 
might  be  paid  and  a  penalty  of  10  cents  for  each  unit  below  im- 
posed, with  the  understanding  that  no  ore  below  40  per  cent, 
would  be  acceptable. 

For  other  methods  of  estimation  of  all  raw  material  used  in 
the  blast  furnace  see  The  Iron  Age,  April  14,  1904,  p.  12. 


50  Blast  Furnace. 

PREPARATION'  OF  ORES. 

By  far  the  greater  proportion  of  ores  come  from  the  mines  in 
such  condition  that  they  may  be  charged  into  the  furnace  at  once. 
Certain  kinds,  however,  must  be  put  through  some  preliminary 
process  in  order  to  render  them  more  tractable  in  the  furnace. 
The  most  usual  preparatory  processes  are  calcination,  roasting, 
concentration  and  agglomeration. 

CALCINATION. 

Calcination  of  ores  has  two  objects,  namely: 

(1)  To  prepare  them   for   better   reduction   by   changing 

their  physical  properties,  either 

a)   by  removing  water  from  hydrous  ores; 

b)  by  removing  CCX  from  spathic  ores, 

c)  by  making  dense  ores  more  permeable  to 

gases. 

(2)  To  render  the  ore  magnetic,  in  order  to  facilitate  sub- 

sequent concentration. 

(la)  Usually  the  removal  of  water  alone  by  calcination  is 
superfluous,  as  the  water  is  readily  evaporated  in  the  top  of  the 
furnace  by  heat  that  would  otherwise  be  wasted. 

(ib)   The  removal  of  carbon  dioxide  before  charging  is  more 
imperative.     According  to  Wedding,  carbon  dioxide  can  be  com- 
pletely eliminated  from  ferrous  carbonate  by  heat,  either  with  or 
Jnis96?ii!;    without  access  of  air.     The  reactions  are  slightly  different,-  how- 
''   ever.    With  access  of  air,  FeCO3  decomposes  as  follows  : 

6FeCO3  +  30  =  3Fe2O3  +  6CO2. 
Without  air,  the  reaction  runs  thus : 

6FeCO8  =  FeGO7  +  5CCX  +  CO. 

The  expulsion  of  CO2  from  FeCO3  absorbs  465  B.  T.  U.  per 
pound  of  carbonate.  Hence,  it  should  be  done  outside  of  the  fur- 
nace, where  the  necessary  heat  can  be  produced  more  cheaply. 

(ic)  Calcining  oxide  ores  is  beneficial  only  to  the  physical 
condition  of  the  ores.  It  may  facilitate  the  reduction  of  dense  ores 
by  making  them  more  accessible  to  the  furnace  gases.  This  is 
especially  true  of  magnetites  having  dark  gangue  material,  as  that 
usually  indicates  a  ferrous  silicate,  which  is  capable  of  oxidation. 
Ores  which  can  be  broken  onlv  with  difficulty  before  calcination 


Materials  of  Manufacture.  51 

are  sometimes  disintegrated  completely  by  the  operation.  The  de- 
gree of  oxidation  of  the  ore  will  depend  upon  the  temperature  of 
the  treatment.  Heating  Fe2O3  to  high  temperatures  in  air  will 
produce  Fe3O4  or  FeGO7,  which  are  strongly  magnetic.  Con- 
tinued heating  in  air  for  sufficient  period  at  low  redness  will 
restore  the  original  Fe2O3  and  the  magnetic  property  will  be  lost. 
The  reduction  of  Fe2O3  in  the  furnace  is  more  easy  than  that  of 
Fe3O4  and  Fe6O7.  Yet  for  certain  reasons  these  compounds  may 
be  necessary.  If  it  is  desirable  to  concentrate  the  ore  by  means 
of  magnets,  these  magnetic  oxides  are  essential,  since  Fe2O3  is 
only  slightly  susceptible  to  magnetism,  and  FeO  cannot  be  pro- 
duced commercially. 

At  Wharton,  N.  J.,  the  Hibernia  ore,  a  dense  magnetite,  is 
calcined  with  gas  in  a  Davis-Colby    kiln    for    the    purpose    of    ue°  nf^'o 
changing  it  to  Fe2O3  and  thereby  rendering  it  more  susceptible 
to  furnace  reactions. 

(2)  Calcination  for  the  purpose  of  rendering  ores  magnetic 
is  unnecessary  in  the  case  of  magnetites,  as  they  are  already 
magnetic.  Spathic  ores,  as  we  have  seen,  when  decomposed  in 
a  neutral  atmosphere,  yield  the  magnetic  oxide,  FeGO7.  If  they  |,8^6IL 
are  decomposed  at  sufficiently  high  temperatures  in  air,  they 
will  yield  Fe3O4. 

Hematites  may  be  rendered  magnetic  in  two  ways. 

a)  By   heating  strongly    in    the    absence   of   air,    oxygen    is 
liberated  thus : 

3Fe2O3  =±  2Fe3O4  +  O  —  Fe6O7  +  zO. 

The  temperature  must  be  very  high,  and    it    is    difficult    to 
prevent  sintering  of  the  more  fusible  components. 

b)  By  heating  in  the  presence  of  reducing  agents,  some  of 
the  oxygen  may  be  removed  at  moderate  temperatures,  leaving 
the  residue  magnetic.    This  may  be  accomplished  by  the  use  of 
solid  carbonaceous  matter,  or  by  means  of  reducing  gases,  such 
as  carbonic  oxide  or  hydrogen,  or  by  means  of  water  or  producer- 
gases,  which  contain  them.    Limonites  and  brown  hematites,  when 
dehydrated,  act  very  much  as  hematites.     They  are  more  easily 
attacked,  owing  to  their  porosity. 

The  calcination  of  lump  ore  is  best  performed  in  vertical 


52  Hlnst  Furnace. 

shaft  furnaces  with  a  good  batter  to  facilitate  the  descent  of 
the  ore.  The  air  for  the  combustion  of  the  fuel  should  be  so 
regulated  that  it  consumes  only  enough  of  the  fuel  to  keep  up 
the  necessary  temperature,  thereby  leaving  a  residue  to  act  as  a 
reducing  agent.  The  desirable  temperature  is  dependent  upon 
the  composition  of  the  ore.  If  the  gangue  is  fusible,  moderate 
temperatures  must  be  used. 

Since  the  magnetization  of  a  piece  of  ore  must  proceed  from 
the  outside  inward,  the  lumps  must  not  be  too  large,  or  the  action 
will  be  incomplete,  or  unnecessary  time  will  be  consumed.  On 
the  other  hand,  fine  ores  are  difficult  to  magnetize  uniformly,  as 
the  gases  make  channels  in  the  ore,  through  which  they  pass, 
leaving  untouched  material  on  either  side.  Finally,  it  is  desirable 
that  the  material  should  be  approximately  uniform  in  size,  in 
order  that  the  fine  material  may  not  clog  the  spaces  between  the 
coarse,  and  thereby  impede  the  free  passage  of  the  gases. 

ROASTING. 

The  object  of  roasting  is  the  removal  of  sulphur.  It  consists 
essentially  of  heating  the  ore  to  a  high  temperature  with  contact 
of  air.  The  sulphur  is  present  usually  as  pyrite,  which  has  the 
formula  FeS2,  showing  that  two  atoms  of  sulphur  are  in  combina- 
tion with  one  of  iron.  One  of  the  atoms  of  sulphur  is  loosely  at- 
tached and  can  be  expelled  by  simply  heating  without  contact  of 
air,  thus: 

FeS2  =  FeS+S. 

The  elemental  sulphur  thus  liberated  escapes  by  volatilization. 
Heat  alone  is  insufficient  to  decompose  the  FeS  which  remains. 
By  the  addition  of  oxygen  from  the  air,  however,  a  further 
change  takes  place,  and  ferrous  sulphate  is  formed,  thus: 

FeS  +  2O2  =  FeSO4. 

Further  heating  completely  decomposes  the  sulphate,  forming 
oxide  with  the  liberation  of  sulphur  dioxide  and  oxygen,  thus: 

2FeS04  ==  Fe203  +  2SO2  +  O. 

These  two  conditions  are  well  illustrated  by  experiments  by 
Valentine, 


Materials  of  Manufacture.  53 

S  as  sulphide 

Temperature.     Time,  S  lost.       in  residue. 

Substance.  Atmosphere.  degrees  F.        hours,          Per  cent.      Per  cent.       Tr  A  L  M  E 

Pyrite With  air.  3,200  4  98  49  XVIIL,  p.  78. 

Pyrite 3CCM-1CO2  1,800  4  37  99 

Pyrite ...  .Without  air.  2,500  18  44  99 

From  these  experiments  the  following  conclusions  are  evident : 

1.  Sulphur  is  almost  completely  removed  from  FeS2  by  heat- 
ing in  air  at  moderate  temperatures. 

2.  Prolonged  heating  of   FeS2  at  high  temperatures  out  of 
contact  with  air  or  in  an  atmosphere  of  furnace  gases  will  not 
remove  over  50  per  cent,  of  the  sulphur. 

3.  The  sulphur  in  the  slight  residues  of  (i)  exists  largely  in 
the  condition  of  sulphate ;  the  sulphur  in  the  heavy  residues  of 
(2)   and   (3)   exists  as  practically  unchanged  sulphide. 

Although  these  experiments  were  made  on  pure  pyrite,  they 
serve  well  to  illustrate  the  general  effects  of  roasting. 

Experiments  in  roasting  Cornwall  ore,  containing  2.66  per 
cent.  S.  in  the  presence  of  air  under  varying  conditions  gave  these 
results. 

S  as  sulphide 

Temperature,  Time,  S  lost.  in  residue. 

Ore.                            Per  cent.  S.          degrees  F.  hours.  Per  cent.  Per  cent. 

Cornwall 2.66                  1,200                  2  87  32             Ibld. 

Cornwall 2.66                   1,200                   4  93  51 

Cornwall 2. CO                  1,500                  1  96  72 

Cornwall 2.66                  2,400                    %  9  3V2 

From  these  figures  it  appears  that  the  higher  the  temperature 
and  the  longer  the  exposure  at  a  given  temperature,  the  more  com- 
plete the  elimination,  within  certain  limits.  If  the  temperature  is 
raised  high  very  suddenly,  as  in  the  fourth  experiment,  the  sul- 
phide fuses,  thereby  retarding  oxidation  and  preventing  volatili- 
zation. The  prime  requisites  for  successful  roasting  are  control 
of  temperature  and  excess  of  air. 

Operation — In  roasting  ores  on  a  large  scale  as  a  prepara- 
tion for  smelting,  it  is  desirable  to  have  a  temperature  sufficient 
for  successful  oxidation  with  the  least  expenditure  of  fuel.  Solid, 
liquid  or  gaseous  fuel  may  be  used.  The  solid  fuel  is  mixed  with 
the  charge  of  ore  in  a  suitable  kiln  and  caused  to  burn  in  contact 
with  the  ore.  In  this  way  the  ore  may  be  roasted  in  tolerably 
thick  bodies.  Liquid  and  gaseous  fuels  are  burned  in  a  com- 


54  Blast  Furnace. 

bustion  chamber  at  one  side  of  a  comparatively  thin  body  of  ore. 
The  products  of  combustion  pass  through  the  column  on  the  way 
to  the  chimney. 

An  example  of  the  first  kind  of  roaster  is  the  Gjers  kiln,  or 
Cleveland  Calciner,  as  it  is  used  in  the  Cleveland  iron  district  of 
England,  and  at  Lebanon,  Pa.  It  consists  of  a  cylindrical  steel 
plate  jacket  contracted  toward  the  bottom,  where  it  is  provided 
with  outlets  for  the  product  and  inlets  for  air.  The  whole  is  then 
lined  with  fire  bricks.  According  to  Turner,  such  a  kiln,  33  feet 
Monlr"!f"  m&h  and  w*tn  24  ^eet  diameter,  would  have  a  weekly  capacity  of 
p>  18<  nearly  1000  tons.  The  ore,  mixed  with  about  5  per  cent,  of  small 
coal,  is  charged  at  intervals  at  the  top  and  withdrawn  at  the 
bottom.  The  rate  of  progress  depends  upon  the  rate  of  with- 
drawal, but  it  should  not  exceed  about  12  feet  per  day,  which  is 
equivalent  to  a  daily  product  of  about  140  tons.  As  used  at 
Cornwall,  Pa.,  the  roasters  ranged  from  10  feet  to  20  feet  high, 
and  12  to  22  feet  in  diameter,  and  used  50  to  100  pounds  coal 
TF.  A.  i.  M.E.,  per  ton  of  ore,  roasting  10  to  56  tons  per  day,  according  to  the 
size  of  kiln.  The  time  of  treatment  was  from  two  to  ten  days, 
and  the  cost  ranged  from  20  to  /o  cents  per  ton.  The  average 
was  30  cents ;  12  cents  for  fuel  and  18  for  labor. 

An  example  of  the  second  type  of  roaster  is  the  Davis-Colby 
kiln,  which  is  largely  used  for  the  ores  of  Cornwall,  Pa.  The 
earlier  form  of  this  kiln  consisted  of  a  central  cylindrical  flue, 
which  led  to  the  chimney,  and  was  surrounded  by  an  annular 
space,  about  18  inches  wide  at  the  top,  and  increasing  slightly 
downwards.  Firebrick  walls  enclosed  the  annular  space,  and 
separated  it  from  the  central  flue.  The  ore  was  charged  in  the  top 
xvm.,  P.  303!  of  the  annular  space,  and  gas  and  air  were  admitted  through  the 
surrounding  wall.  The  gas  burned  in  a  combustion  chamber,  and 
the  products  of  combustion  were  drawn  through  the  ore  into  the 
central  flue  by  the  draught  of  the  chimney.  The  roasted  ore  was 
withdrawn  at  the  bottom. 

A  comparison  of  results  produced  by  this  method  with  those 
of  the  Gjers  kiln  when  both  were  working  on  the  Cornwall  ore 
showed  a  decided  advantage  in  favor  of  the  gas  method.  The 
sulphur  is  more  nearly  eliminated,  and  what  remains  is  more  fully 
changed  to  sulphate,  thus : 


Materials  of  Manufacture.  55 

Per  cent.  S  Per  cent.  S  Per  cent.  S 

Kiln.  in  product.  as  sulphate.  as  sulphide. 

Gjers...  ..SI. 133  24.08  75.02 

(1.3KO  9.78  90.22 

Average     1.250  17.38  82.62    Ibid- 

f  0.782  54.21  45.79 

Davis-Colby ' .  . -i  0.798  39.85  60.15 

[0.596  49.14  50.86 

Average     0.725  47.73  52.27 

More  recent  experiments  show  results  as  low  as  0.3  to  0.4  per 
cent.  S.,  with  an  average  of  0.8  to  0.9  per  cent. 

The  later  forms  of  the  Davis-Colby  kilns  are  rectangular  in 
shape  and  of  large  dimensions.  The  kiln  at  Wharton,  N.  J.,  is 
100  feet  long  by  36  feet  wide,  having  receiving  bins  on  top  and 
discharge  chutes  beneath.  Three  lines  of  standard  gauge  tracks 
run  along  the  top  of  the  bin,  55  feet  from  the  ground.  The  body 
of  the  kiln  is  raised  from  the  ground  19  feet,  to  permit  of  the  con- 
struction of  chutes,  which  discharge  the  roasted  ore  into  railroad 
cars.  It  is  built  in  duplicate  and  consists  of  two  rectangular  cham- 
bers the  length  of  the  kiln,  24  feet  deep  and  about  12  feet  wide. 
These  chambers  are  divided  longitudinally  by  two  brick  walls, 
making  three  spaces  which  connect  at  intervals.  The  middle  one, 
which  has  a  slight  batter  downward,  is  the  ore  chamber.  The  outer 
space  serves  as  a  combustion  chamber  and  is  fed  from  a  supply 
pipe  by  numerous  gas  burners  at  intervals  near  the  bottom.  The 
inner  space  serves  as  a  collecting  chamber  for  the  products  of 
combustion  which  have  passed  through  the  ore.  The  two  inner 
chambers  connect  with  a  central  flue  that  leads  to  the  chimney. 
This  kiln  is  used  to  calcine  dense  magnetic  ores,  to  render  them 
porous.  It  is  said  to  treat  600  to  800  tons  per  day  at  a  temperature 
of  about  1 200  degrees  F.  Similar  kilns  are  in  use  at  Lebanon 
also,  for  roasting  sulphurous  ore. 

CONCENTRATION. 

The  concentration  of  ore  has  two  objects,  which  may  or  may 
not  be  simultaneous,  namely,  enrichment,  and  the  removal  of  ob- 
jectionable substances.  Concentration  may  be  of  two  kinds,  wet 
or  dry. 

Wet  concentration  is  usually  applied  to  ores  which  contain 


50 


Blast  Furnace. 


Davis-Colby  Kiln  at  Wbarton,  N.  J. 


Materials  of  Manufacture.  57 

clay,  pebbles  or  sand.     It  may  be  of  two  kinds,  namely,  wash- 
ing and  jigging.     The  washing  process  is  applicable  to  ores  in 
which  clay  is  the  objectionable  constituent.     The  usual  form  of 
washery  consists  of  a  log,  carrying  numerous  fins  or  scrapers  on   Tr  A  L  M  E> 
its  surface,  and  revolving  in  an  inclined  trough  which  is  plenti-    XXIV-.*»-34- 
fully  supplied  with  water.     The  ore  which  is  charged  into  the 
lower  end  of  the  trough  is  constantly  worked  by  the  revolving 
fins  toward  the  head  of  the  trough,  where  it  is  discharged,  and 
the  clay,  after  being  thoroughly  disintegrated  by  the  fins,  is  car- 
ried off  by  the  water  at  the  foot  of  the  trough. 

Ores  which  contain  pebbles  or  sand  must  be  treated  by  the 
jigging  process,  since  the  particles  are  too  heavy  to  be  carried 
away  by  gently  flowing  water.  The  jigs  consist  of  boxes  with 
perforated  bottoms,  set  in  tanks  of  water.  The  water,  pulsating 
rapidly  through  the  perforations,  causes  the  different  particles 
in  the  boxes  to  separate  into  layers  according  to  their  respective 
specific  gravities.  The  ore  collects  on  the  bottom,  that  which  is  XI'IL,  p.  35.  ' 
fine  enough  passes  through  the  perforations  into  the  tank,  while 
the  pebbles  and  sand  which  lie  on  top  are  allowed  to  overflow 
and  go  to  waste.  Both  washing  and  jigging  find  their  chief 
application  in  the  local  ores  of  Pennsylvania,  Virginia  and  Ala- 
bama. Washing  is  much  more  widely  practised  than  jigging,  but 
even  washing  is  applied  to  only  a  very  small  percentage  of  the 
ores  used. 

Dry  Concentration. — Dry  concentration  usually  takes  the 
form  of  magnetic  separation.  The  application  of  this  process  de- 
pends upon  the  fact  that  all  ores  are  magnetic,  or  may  be  made  so. 
When  the  ore  is  crushed  to  such  a  degree  of  fineness  that  the 
compounds  of  iron  are  detached  from  the  gangue  material  and 
the  mixture  is  passed  in  a  thin  layer  before  strong  magnets,  the 
magnetic  particles  are  attracted  away  from  the  non-magnetic,  and 
a  more  or  less  complete  separation  takes  place.  If  the  ore  is  not 
magnetic  it  is  necessary  to  make  it  so  before  applying  this  process. 
Some  ores  may  be  magnetized  simply  by  heating  at  certain  tem- 
peratures, but  generally  it  is  necessary  to  heat  in  the  presence  of 
finely  divided  carbon,  such  as  coal,  or  other  reducing  substances. 
Partial  reduction  of  completely  oxidized  ores  tends  to  make  them 
more  magnetic. 


58  Blast  Furnace. 

There  are  several  types  of  magnetic  separators,  which  differ 
more  in  construction  than  in  principle. 

The  Ball-Norton  "  drum  type  "  separator  consists  of  horizon- 
tal drums  revolving  around  stationary  magnets  which  act  through 
the  lower  third  of  the  drum.     The  ore  is  fed  beneath  the  drums, 
r  \  i  M  E.     wmcn  n°ld  the  magnetic  material,  while  the  tailings  fall  to  the 
xix.,  p.  is:.'   ground.    As  the  drum  rotates,  the  magnetic  material  clinging  to  it 
is  carried  out  of  the  field  of  the  stationary  magnet  and  the  load 
falls  into  a  bin,  or  into  the  hopper  of  the  next  drum. 

The  Wenstrom  separator  also  has  revolving  horizontal  drums, 

but  the  magnets  are  placed  at  the  side  instead  of  the  bottom.    The 

ore  drops  to  the  magnetized  area,  whereupon  the  tailings  fall  to 

P.  65.'    the  ground,  while  the  magnetic  particles  are  attracted  to  the  drum 

and  carried  to  a  bin  beneath  it. 

The    Buchanan     separator   consists   of   two   rolls    revolving 

toward  each  other  and  connected  by  a  horseshoe  magnet.     The 

ore  is  fed  between.    The  non-magnetic  tailings  fall  to  the  ground, 

'    while  the  magnetic  particles  cling  to  the  rolls  and  are  conveyed  to 

bins  beneath. 

The  Ball-Norton  "  belt-type  "  magnetic  separator  is  in  use  at 
Mineville,  New  York,  where  it  is  said  to  surpass  the  drum  type 
in  capacity  and  efficiency,  beside  being  cheaper  to  construct  and 
maintain.  It  consists  of  a  series  of  twelve  magnets  of  alternate 
polarity,  placed  side  by  side  above  a  moving  belt,  which  is  well 
NOV.™  IMS,'  within  the  magnetic  zone.  A  feed  belt  running  on  a  slightly  lower 
level  brings  the  material  under  the  magnetized  belt,  as  far  as  the 
third  magnet.  The  magnetic  particles  adhere  to  the  under  side  of 
the  magnetized  belt,  while  the  non-magnetic  material  is  carried  on 
to  the  tailings  bin.  The  magnetic  portion  is  conveyed  to  its  bin 
across  the  faces  of  the  magnets,  and  is  turned  end  over  end  by 
their  alternating  polarity.  This  action  tends  to  free  entrained 
non-magnetic  particles,  thereby  making  a  purer  product.  Each 
machine  is  said  to  be  able  to  work  30  tons  per  hour. 

The    Wetherill  separator  is  made  in  two  distinct  types,  both 
of  which  are  used  at  Mineville. 

The   "  roller "   type,   which   is  designed   for  the   selection   of 
strongly  magnetic  material,  consists  essentially  of  a  horizontal 


Materials  of  Manufacture. 


59 


roller  revolving  between  the  poles  of  a  stationary  electro-magnet. 
The  roller  becomes  strongly  magnetic  through  induction.  The 
crushed  ore  is  fed  on  the  top  of  the  roller  and  is  carried  by  the 
revolution  into  the  line  of  magnetism.  The  non-magnetic  min- 
erals fall  from  the  roller  into  the  tailings  chute,  and  the  magnetic 
portion  is  carried  forward  to  the  neutral  point,  where  it  drops 
into  the  concentration  chute.  Machines  are  built  to  operate  on  6, 
14  and  30  amperes  at  no  volts,  and  are  said  to  handle  400  tons 
per  24  hours. 

The  "  cross-belt  "  type,  designed  for  selecting  weakly  magnetic 


The  Wetherill   Magnetic  Separator,  Type  E. 

minerals,  consists  of  two  horseshoe  electro-magnets,  placed  hori- 
zontally with  poles  facing,  the  pole  pieces  on  the  upper  magnet 
being  wedge-shaped,  and  those  on  the  lower,  flat.  Between  the 
magnets  runs  a  horizontal  belt  which  carries  the  material.  Be- 
neath each  of  the  wedge-shaped  poles  and  just  above  the  material 
runs  a  small  cross-belt.  The  paramagnetic  minerals  jump  toward 
the  wedge-shaped  pole  where  the  lines  of  force  are  concentrated. 
They  adhere  to  the  underside  of  the  cross-belts  and  are  carried 
rut  of  the  magnetic  field,  where  they  drop  by  gravity.  The 
uamagnetic  materials  are  carried  on  by  the  feed  belt  to  the  tailings 
£in.  This  type  is  made  in  capacities  ranging  from  6  to  30  am- 
at  no  volts  pressure. 


60  Blast  Furnace. 

Magnetic  concentration  of  iron  ores  has  been  most  fully  de- 
veloped in  this  country  at  Mineville,  where  the  operation  is  car- 
ried out  on  two  grades  of  ore ;  in  one  case  for  the  purpose  of 
enrichment,  in  the  other  in  order  to  separate  an  undesirable  con- 
stituent. The  two  grades  are :  ( i )  The  Old  Bed  ore,  which  con- 
sists of  magnetite  already  rich  in  iron,  but  containing  a  prohibitive 
amount  of  phosphorus,  and  (2)  the  New  Bed  and  Harmony  ores, 
which  are  a  low  grade  magnetite  with  a  moderate  amount  of  phos- 
phorus. The  results  of  concentration  of  Old  Bed  ores  are  a  very 
rich  concentrate,  reasonably  low  in  phosphorus,  and  tailings  lo\v 
in  iron,  but  high  enough  in  phosphorus  to  have  a  value  as  fer- 
tilizers. The  results  of  concentrating  the  New  Bed  and  Harmony 
ores  are  a  rich  concentrate  with  still  lower  phosphorus  and  value- 
less tailings.  Fortunately,  the  ores  are  of  granular  structure  and 
the  phosphorus  exists  in  the  form  of  apatite,  or  calcic  phosphate, 
which  is  more  or  less  completely  freed  from  the  oxide  of  iron  by 
crushing.  The  method  of  procedure  is  to  crush  the  ore  so  that  it 
will  all  pass  a  six  mesh  screen.  The  crushing  is  done  by  means 
of  a  Blake  rock  crusher  and  a  set  of  Reliance  rolls.  The  crushed 
ore  is  then  separated  by  screening  into  portions  that  will  pass 
DeJ.7"  i&,  through  the  30,  16,  10  and  6-mesh  screens  respectively.  These 
are  then  dried  in  an  Edison  drying  tower  and  sent  to  Rowand 
and  Ball-Norton  magnetic  separators.  The  tailings  from  this 
operation  are  sized  again  to  16  and  20  mesh,  and  re-treated  on 
the  Wenstrom  and  Wetherill  magnetic  separators.  The  oversize 
is  crushed  again  in  a  set  of  Reliance  rolls,  and  re-treated.  The 
plants  for  treating  the  Old  Bed  and  Harmony  ores  are  practically 
duplicates,  and  the  results  of  each  are  summarized  below. 

Product.                                                               Per  cent.  Fe.  Per  cent.  P.  Per  cent.  ore. 

Old  Bed  ore 59.59                   1.74  100.0 

Iron  concentrates 67.34                  0.675  85.0 

No.  1  phosphate  concentrates 3.55                12.71  7.5 

No.  2  phosphate  concentrates 12.14                   8.06  7.5 

Harmony  ore 50.26  0.295  100.0 

Iron   concentrates 64.10  0.133  77.0 

Tailings    13.97  0.877  23.0 

A  somewhat  different  method  of  procedure  is  in  use  at  Hi- 
bernia,  New  Jersey.  The  ore  is  passed  first  through  a  Buchanan 
crusher  and  set  of  rolls,  and  crushed  to  a  size  which  will  pass  a 


Materials  of  Manufacture.  61 

2  3/2 -inch  screen.  It  is  then  passed  over  a  Ball  magnetic  separator,  o 
having  the  low  potential  of  13  volts,  which  selects  the  richest  of  p'16' 
the  ore,  giving  a  coarse  concentrate.  The  tailings  from  this  opera- 
tion are  passed  more  slowly  over  a  more  powerful  magnet  of  25 
volts  potential,  which  selects  all  that  is  worthy  of  further  treat- 
ment. The  tails  from  this  stage  are  allowed  to  go  to  waste,  while 
the  heads  are  recrushed  and  passed  over  a  third  separator  having 
a  potential  of  15.  This  operation  yields  the  fine  concentrates. 
This  differential  method  of  separation  saves  much  expense 
of  crushing,  and  leaves  the  concentrates  in  a  coarse  condition, 
suitable  for  charging  without  agglomerating.  The  operation  as  car- 
ried out  at  Hibernia,  on  an  ore  containing  only  47  per  cent,  iron, 
yields  concentrates  containing  60  per  cent,  iron,  and  tailings  that 
carry  only  15  per  cent. 

AGGLOMERATION. 

A  very  grave  objection  to  fine  ore  is  its  tendency  to  be  carried 
out  of  the  furnace  top  by  the  escaping  gases.  This  feature  be- 
comes more  marked  with  high  pressures  of  the  blast  and  rapid 
driving  of  the  furnace.  For  this  reason  fine  ore  is  sometimes  put 
through  the  process  of  agglomeration.  This  consists  of  assem- 
bling the  fine  particles  into  balls  or  cakes,  which  are  held  together 
by  some  adhesive. 

Briquetting. — When  admixed  adhesives,  such  as  fused  slag, 
milk  of  lime,  coal  tar,  rosin,  molasses,  malt  liquors,  glutens  and 
various  commercial  preparations  are  used  as  binders,  the  process 
is  called  "  briquetting."  A  suitable  binder  must  make  briquettes 
that  can  be  handled  roughly  without  breaking  or  crumbling,  that 
can  stand  changes  in  weather,  and  that  will  not  be  detrimental  to 
the  furnace  or  its  product.  The  method  of  manufacture  consists 
of  mixing  the  required  proportion  of  the  binder  thoroughly  with 
the  ore  in  a  pugmill  or  other  suitable  device,  of  passing  the  mix- 
ture into  a  moulding  machine,  such  as  a  brick  press,  which  gives 
it  shape,  and  finally  of  drying  the  briquettes  in  a  suitable  oven. 
Up  to  the  present,  however,  briquetting  has  not  proved  a  com- 
mercial success. 

Nodulizing — The  process  of  nodulizing  fine  ores  as  devel- 
oped by  the  National  Metallurgical  Company,  of  New  York,  con- 


62 


Blast  Furnace. 


Sep!t?i905'  sists  in  passing  fine  ores,  flue  dust,  etc.,  through  a  rotary  kiln  at 
high  temperatures.  The  kiln  consists  of  a  shell  of  steel  plates,  riv- 
eted together  and  lined  with  bricks.  It  is  set  at  a  slight  inclination 
from  the  horizontal,  and  is  100  feet  long  by  6  feet  diameter  at 
the  feed  end  and  7  feet  at  the  discharge  end.  The  ore,  mixed 
with  i  per  cent,  of  tar,  is  delivered  by  an  automatic  feeder  into 
the  upper  end,  and  finely  powdered  and  dried  coal  is  blown  in  by 
a  blast  at  the  lower  end.  The  ore  is  il/2  hours  passing  through 
the  kiln,  and  is  discharged  in  the  form  of  sintered  and  purified 
nodules.  The  size  of  the  nodules  may  be  varied  by  varying  the 
temperature,  the  quantity  of  tar  and  the  speed  of  revolution. 
The  tar  serves  as  a  binder  until  nodulizing  begins,  when  it  volatil- 
izes, taking  with  it  much  of  the  sulphur  and  arsenic,  and  leaving 
the  product  very  nearly  pure.  The  plant  treats  175  tons  in  24 
net.  jour.,  hours,  at  an  expenditure  of  150  horsepower.  The  product  is  in  a 
P.  358.'  granular  to  slightly  lumpy  condition,  admirably  adapted  to  use 


in  the  furnace. 


ORES   OF  THE   UNITED   STATES. 


The  ores  of  the  United  States  which  have  commercial  value 
are  of  three  kinds,  hematites,  limonites  and  magnetites. 

In  the  northern  states,  the  ores  used  are  chiefly  hematites  from 
the  rich  deposits  of  the  Lake  Superior  districts.  These  ores  are 
red  hematites,  though  sometimes  hydrous.  They  average  54  per 
cent,  metallic  iron,  with  little  gangue,  and  require  no  preparation. 
This  enables  them  to  compete  with  poorer  local  ores  in  all  the 
northern  furnace  districts.  In  some  localities,  however,  the  native 
supply  of  brown  hematites  still  furnishes  a  portion  of  the  ores 
used.  In  the  eastern  district,  notably  New  York  and  New  Jersey, 
a  considerable  quantity  of  magnetites  is  mined  for  local  use. 
These  ores  are  sometimes  used  as  they  come  from  the  mine,  and 
sometimes  are  subjected  to  preparatory  operations. 

In  the  southern  states,  especially  in  Alabama,  the  ore  supply 
is  of  two  kinds,  hematite  and  limonite.  The  hematites  are  of 
Clinton  age,  and  above  water-level  exist  as  soft  and  tolerably  rich 
ores.  In  depth  they  are  leaner,  and  are  associated  with  12  to 
20  per  cent,  limestone,  which  renders  them  almost  self-fluxing. 
The  limonite  ores  are  of  better  quality,  although  they  must  be 


Materials  of  Manufacture.  63 

subjected  to  washing  before  use.  They  average  nearly  50  per 
cent,  metallic  iron. 

Hematite    Production During   1907,   46,060,486   tons   of 

hematite  ore,  amounting  to  89  per  cent,  of  the  total  production, 
was  mined  in  the  United  States.  Of  this  amount,  56  per  cent,  came 
from  Minnesota,  23  per  cent,  from  Michigan  and  the  remainder 
from  Alabama,  Wisconsin  and  Tennessee.  Over  90  per  cent, 
of  all  the  hematite  produced,  viz.,  41,604,454  tons,  was  produced 
by  what  is  commonly  known  as  the  "  Lake  Superior  district." 
This  district  lies  to  the  southwest  and  north  of  Lake  Superior,  and 
includes  the  northern  portions  of  Michigan,  Wisconsin  and  Min- 
nesota, and  part  of  Canada.  There  are  five  distinct  groups  of 
mines  or  ranges.  Their  relative  shipments  in  1906,  1907  and  1908 
were  as  follows : 

1906.  1907.  1908. 

Long  tons.  Long  tons.  Long  tons. 

Mesaba     23,819,029  27,495,708  17,257,350 

Menominec 5,109,088  4,964,728  2,679,156 

Marquette    4,057,187  4,388,073  2,414,632 

Gogebic    3,643,514  3,637,102  2,699,856 

Vermilion 1,792,355  1,685,267  841,544 

Totals 38,421,173  42,170,878  25,892,538 

Of  these  five  ranges,  the  Mesaba,  although  by  far  the  most 
productive,  is  of  comparatively  recent  development,  and  of  radi- 
cally different  character  from  the  others.  The  other  four  are  gen- 
erally referred  to  as  the  "  old  ranges  "  to  distinguish  them  from 
the  Mesaba. 

The  first  range  to  be  developed  was  the  Marquette.  It  is  situ- 
uated  in  the  upper  peninsula  of  Michigan,  with  its  eastern  extrem- 
ity on  the  lake  shore  at  Marquette,  which  serves  as  its  shipping- 
point.  It  extends  westward  for  a  distance  of  about  30  miles. 
It  is  most  actively  developed  in  the  vicinity  of  the  towns  of  Ne- 
gaunee,  Ishpeming  and  Champion.  There  is  considerable  produc- 
tion also  at  Republic,  a  few  miles  south  of  Champion.  This 
region  was  discovered  in  the  forties,  and  became  an  important 
producer  in  1854.  The  ores  are  both  hard  and  soft.  The  hard 
ores  are  massive  or  specular  hematites,  and  must  be  drilled  and 
blasted,  thus  forming  lump  ore.  The  soft  ores  are  somewhat 
hydrated,  and  resemble  limonite.  Both  Bessemer  and  non-Besse^ 
mer  ores  are  produced. 


64  Must  FitriHicc. 

The  Menominee  Range  was  opened  in  1877.  It  is  loeated  in 
the  vicinity  of  the  Menominee  River,  in  both  Michigan  and  Wis- 
consin. The  most  active  operation  is  at  Iron  Mountain,  Michigan, 
which  is  about  40  miles  south  of  the  Marquette  group,  and  about 
the  same  distance  from  the  ports,  Escanaba  and  Marquette, 
which  serve  as  shipping  points.  The  ores  are  generally  soft,  blue 
hematites,  showing  specular  particles. 

The  Qogebic  Range,  which  was  opened  in  1885,  is  situated 
also  on  the  boundary  between  Upper  Michigan  and  Wisconsin, 
about  10  miles  from  Lake  Superior  and  about  100  miles  from 
Marquette.  It  is  about  20  miles  in  length,  and  is  most  actively 
worked  at  Bessemer  and  Ironwood,  in  Michigan,  and  at  Hurley, 
Wisconsin.  The  ores  of  these  deposits  are  soft  blue,  brown,  and 
black  hematites,  often  high  in  manganese,  and  practically  all 
Bessemer. 

The  Vermilion  Range,  which  was  also  discovered  in  1885,  is 
quite  remote  from  the  three  preceding  ranges.  It  is  located  in 
northeastern  Minnesota,  about  75  miles  due  north  from  Duliilh. 
It  has  two  points  of  development,  namely,  at  Soudan,  near  Tower, 
and  at  Ely,  about  20  miles  northeast  of  Tower.  The  ore  found 
at  Soudan  is  hard,  dense,  somewhat  specular  hematite.  It  is  ex- 
ceedingly difficult  to  drill.  Part  is  Bessemer  and  part  is  non- 
Bessemer.  At  Ely  the  ores  are  all  soft  and  of  good  Bessemer 
quality. 

The  Mesaba  Range,  which  is  now  such  a  heavy  producer  of 
iron  ore,  did  not  become  a  factor  until  1893.  It  differs  materially 
from  the  older  ranges.  Its  location  is  about  20  miles  southwest 
from  Tower,  and  about  60  miles  from  Duluth.  It  is  about  40 
miles  long,  arid  has  important  developments  at  Biwabik,  Virginia, 
Mountain  Iron  and  Hibbing.  The  ores  are  red,  brown  and  yel- 
low, of  soft,  loamy  texture,  and  sometimes  of  extreme  fineness. 
They  are  easily  carried  out  of  the  furnace  by  the  gases,  and  they 
also  cause  a  deposition  of  carbon  which  obstructs  the  passage  of 
the  gases.  Some  of  the  ores  are  of  Bessemer  quality. 

The  Clinton  or  Fossil  Ores  derive  their  names  from  Clinton, 
N.  Y.,  where  they  were  formerly  of  considerable  economic  im- 
portance, and  from  the  fact  that  they  contain  many  fossil  remains 


Materials  of  Manufacture.  65 

of  the  Upper  Silurian  Age.  They  occur  interstratifiecl  with  shales 
and  limestone.  They  are  scattered  over  a  very  wide  area  and  are 
remarkably  persistent.  Wherever  the  Clinton  stage  appears,  one 
or  more  beds  of  ore  is  present.  The  Clinton  ore  has  reached  its 
greatest  economic  development  in  the  Birmingham  district  in 
Alabama,  where  folds  and  faults  have  brought  the  ore  beds  into 
close  proximity  to  the  coal  and  limestone  of  the  region,  thus 
making  the  working  very  economical.  Besides  in  Alabama,  they 
have  economic  importance  in  East  Tennessee,  Northwest  Georgia, 
Southwest  Virginia,  Maryland,  Central  Pennsylvania,  and  New 
York.  They  appear  also  in  Kentucky,  Ohio,  and  Wisconsin. 
The  structure  of  the  ore  varies  in  the  different  localities,  some- 
times appearing  as  a  replacement  of  fossils,  again  as  oolitic  con- 
cretions, and  again  as  ferruginous  limestone.  No  less  than  six 
separate  beds  appear  at  times.  The  richness  of  the  deposits  varies 
widely.  They  are  always  too  high  in  phosphorus  to  be  classed  as 
Bessemer  ores. 

Brown  Hematites  and  Limonites. — Next  to  the  Red  Hema- 
tites, although  far  below  them  in  the  amount  produced,  stand  the 
Brown  Hematites.  In  1907,  2,957,477  tons  of  Brown  Hematites 
were  mined.  The  greater  part  of  this  quantity  was  produced  from 
the  Siluro-Cambrian  deposits  of  Alabama,  Virginia  and  Georgia. 
These  deposits  occur  in  the  slates,  schists  and  limestones  of  the 
Cambrian  and  lower  Silurian  systems  of  the  Appalachians.  They 
are  remarkably  persistent  and  extend  from  Vermont  to  Alabama. 
They  appear  with  considerable  economic  importance  in  eastern 
New  York,  Pennsylvania,  central  Maryland,  southwestern  Vir- 
ginia, eastern  Tennessee,  northwestern  Georgia  and  central  Ala- 
bama. This  belt  formerly  had  very  active  development  in  the 
northern  states,  especially  in  Pennsylvania.  It  is  still  worked 
there  to  some  extent,  and  also  in  Virginia  and  Tennessee,  but  its 
greatest  development  is  now  in  Alabama,  where  it  furnishes  a 
large  proportion  of  the  ores  used. 

Limonite  occurs  in  a.  number  of  localities  in  Colorado.  The 
mines  in  Saguache  County  supply  a  part  of  the  ore  used  at  the 
Pueblo  works. 

Bog  Ore  is  the  name  for  the  beds  of  limonite  which  form  in 
pools  of  stagnant  water.  Ferruginous  waters  coming  in  contact 


66  Blast  1-" it  mace. 

with  alkaline  or  carbonated  waters,  precipitate  their  burden  of 
iron  from  solution,  and  in  time  considerable  beds  of  ore  form. 
Such  deposits- exist  in  North  Carolina,  Canada  and  the  West,  but 
are  not  of  present  economic  importance. 

Magnetite. — Xext  in  order  of  importance  comes  magnetite. 
In  1907,  2,679,067  tons  of  magnetic  ore  and  of  magnetic  con- 
centrates were  used  in  the  East.  They  came  mostly  from  eastern 
New  York,  northern  Xe\v  Jersey,  and  Pennsylvania,  where  they 
occur  in  a  series  of  lenses,  roughly  parallel  in  metamorphosed 
crystalline  rocks,  particularly  gneisses.  The  ores  are  usually 
dense  and  hard,  but  show  generally  a  granular,  semi-crystalline 
condition  which  is  favorable  to  cencentration  by  magnetization. 
They  are  generally  non-Bessemer,  but  in  some  instances  may  be 
brought  to  Bessemer  quality  by  concentration,  in  which  a  portion 
of  the  apatite,  which  is  the  phosphorus-bearing  mineral,  is  left 
behind.  In  the  gneisses  of  the  western  counties  of  Virginia  and 
North  Carolina  are  found  magnetite  beds  of  Bessemer  quality. 

A  unique  and  remarkable  deposit  of  magnetic  ore  occurs  at 
Cornwall,  Pa.  It  is  quite  distinct  from  the  gneissic  deposits, 
being  associated  with  green  pyritous  shales.  The  ore  is  a  soft, 
earthy  magnetite  of  low  grade,  but  owing  to  the  interlaminated 
condition  of  the  shales,  it  does  not  lend  itself  readily  to  magnetic 
separation.  It  is  very  low  in  phosphorus  and  is  used  in  Bessemer 
mixtures.  Owing  to  the  presence  of  pyrite  and  chalco-pyrite, 
however,  the  raw  ore  contains  2  to  3  per  cent,  sulphur,  and  is, 
therefore,  roasted  before  smelting.  The  presence  of  the  chalco- 
pyrite  introduces  nearly  I  per  cent,  of  copper  into  all  pig  iron 
which  is  made  entirely  from  these  ores.  This  deposit  has  been 
worked  continuously  for  more  than  a  century,  and  has  yielded 
many  million  tons  of  ore.  It  is  apparently  far  from  exhausted, 
and  now  reaches  an  annual  output  of  three-quarters  of  a  million 
tons. 

In  Colorado  several  magnetic  deposits  are  known,  but  those 
in  Chaft'ee  County  are  the  chief  producers.  They  furnish  a  part 
of  the  or-  smelted  at  Pueblo.  Magnetic  deposits  occur  also  in 
Utah,  California,  and  to  some  extent  in  the  Lake  Superior  districts. 

Immense  quantities  of  iron  are  known  to  exist  in  the  form  of 
titaniferous  magnetites,  notably  in  New  York;  New  Jersey  and 


Materials  of  Manufacture. 


67 


Canada,  and  also  in  North  Carolina,  Minnesota,  Wyoming  and 
California,  but  this  supply  has  not  been  available  because  of  the 
difficulties  hitherto  ascribed  to  the  melting  of  titaniferous  slags. 
These  deposits  are  usually  low  in  phosphorus  and  sulphur,  and 
when  smelted  are  said  to  yield  iron  of  remarkable  excellence. 

Siderite — The  production  of  spathic  iron  ore  in  the  United 
States  is  of  trifling  importance,  amounting  to  only  23,589  tons  in 
1907.  This  form  of  ore  is  the  least  desirable  in  the  furnace,  owing 
to  its  high  content  of  carbon  dioxide  and  consequent  low  content 
of  iron.  It  often  occurs  associated  with  other  carbonates,  espe- 
cially calcic  and  magnesic,  which  makes  the  ore  at  least  partly 
self-fluxing.  It  usually  appears  as  concretions  embedded  in  strata 
of  the  carboniferous  age.  When  the  association  is  with  bitumi- 
nous matter,  such  as  coal  seams,  the  ore  is  known  as  "  black 
band ;  "  when  embedded  in  shales  and  associated  with  much  clay 
it  goes  under  the  name  of  "  clay  ironstone."  The  former  was 
once  of  considerable  importance  in  Pennsylvania,  West  Virginia 
and  Colorado,  and  the  latter  in  New  York  and  Connecticut. 

According  to  the  annual  report  for  1908  of  the  United  States 
Geological  Survey,  the  following  is  the  output  in  gross  tons  of 
iron  ore  from  the  chief  producing  States  and  a  comparison  of 
the  outputs  of  1907  and  1908: 


State.                                    1907.  1908. 

Minnesota    28,969,658  18,652,220 

Michigan    .'. 11,830,342  8,839,199 

Alabama     4,039,453  3,734,438 


New    York 1,375,020  697,473 

Virginia    786,856  692,223 

Tennessee    813,690  635,343 

New  Jersey 549,760  394,767 

Wisconsin  838.744  733,993 

Pennsylvania  837,287  443,161 

Montana,  Nevada,  New 

Mexico,     Utah     and 

Wyoming    819,544  528,625 

Georgia 444,114  321,060 

Arkansas  and   Texas..       118,667  55,966 

Missouri    111,768  98,414 

1905.  1906. 

Total    product 42,526,133  47,749,728 

Imported    845,651  1,060,390 

Exported    208,017  265,240 

Apparent    consumption. ..  .43,433,138  49,355,343 


Kinds  of  ore  in  1907. 

All  red  hematite. 

All  red  hematite. 

77.8  per  cent,  red  hematite. 
22.2  per  cent,  brown  hema- 
tite. 

89  per  cent,  magnetite. 

88  per  cent,  brown  ore. 

67  per  cent,   brown  ore,  33 
per  cent,  red  hematite. 

91  per  cent,  magnetite. 

96  per  cent,  red  hematite. 

84    per    cent,    magnetite,    13 
per  cent,  brown  ore. 

74  per  cent,  red  hematite,  24 

per  cent,  magnetite. 
76  per  cent,   brown  ore,  24 

per  cent,  red  hematite. 
All  brown  ore. 
Brown  and  red  hematite. 


1907. 

51,720,619 
1,229,168 

278,208 
51,880,398 


1908. 

35,983,336 
776.898 
309,099 

36,451,135 


68  K I  cist  Furnace. 

The  following  comparison  by  the  same  authority  of  the  pro- 
duction and  consumption  of  ore  for  the  past  ten  years  is  instruc- 
tive in  showing  the  rapid  increase  of  ferrous  products  in  this 
country : 

Ore  mined.  Pig  made.                                        Ore  mined.  Pig  made. 

Year.                 Gross  tons.  Gross  tons.  Year.                   Gross  tons.  Gross  tons. 

1895 15,957,614  9,446,307  1902 35.554,135  17,821,307 

1896 16,005,449  8,623,127  1903 35.019,308  18,009,252 

1897 17,518,046  9.652,680  1904 27,644,330  16,497,033 

1S98 19,433,710  11,733,934  1905 42,526,133  22,992,380 

1SP9 24,683,173  13,620,703  1906 47.749,728  25,307,191 

1000 27,553,161  13,789,242  1907 51,720,619  25,781.361 

1901 28,887,479  15,878,354  1908 35,983,336  15,936,018 

Foreign  Ores. — In  addition  to  the  native  ores  of  the  United 
States,  some  imported  ore  is  used  in  the  furnaces  along  the  At- 
lantic seaboard  whose  distance  from  ports  is  not  so  great  as  to 
preclude  competition  with  Lake  Superior  ores.  The  chief  sources 
of  imported  ores  are  Cuba,  Spain  and  Newfoundland. 

ANALYSIS  OF  IRON  ORES. 

Hematites. 

Loss 
by 

igni-  Moist- 

Mino  and  locality.        Fe.     SiO2.  A12O3.  CaO.  MgO.  Mn.       P.  S.      tion.    ure. 
*Angeline,  Marquette..  57.94    3.07    1.17    0.13    0.08    0.27  0.040  0.011    1.80  10.78 
*Cleveland  Cliffs,  Mar- 
quette     63.75    3.04    1.95    0.70    0.70    0.34  0.102  0.018    0.65     0.38 

'Champion,  Marquettc.63.44    4.51     2.36    0.32    0.29    0.20  0.060  0.013      ...     0.88 

"Republic,   Marquette. 67.30    1.80    0.42    0.49    0.13    0.55  0.052  0.053  .0.00     0.59 

<Cb.apin,    Menominee..54.08    5.70    1.31    1.15    3.31    0.48  0.060  0.017    3.00     6.96 

*Pewabic,   Menominee.58.35    4.53    0.92    0.37    1.11    0.13  0.008  0.003    0.84     8.58 

*Toledo,    Menominee..45.2024.19    1.05    0.49    1.13    0.10  0.006  0.010    0.95      7.16 

*Ashland,    Gogebic.  .  .53.49    6.34    2.70    0.38    0.24    0.30.  0.040  0.009    2.54  10.70 

•Gary  Empire,  Gogebic.52.47    5.56    0.79    0.17    0.26    2.26  0.053  0.005    4.77  10.16 

'Chandler,  Vermilion .  60.92    3.97    2.08    0.60    0.13    0.21  0.038  0.002    0.85     5.54 

'Vermilion,  Vermilion  .65.39    2.56    0.84    0.62    0.30    0.04  0.086  Tr.      0.30     1.56 

'Biwabik,  -Mesaba 56.93    3.67    1.21    0.24    0.10    0.45  0.040  0.008    3.88     8.75 

"Elba,    Mesaba 56.57    3.60    0.86    0.12    0.06    1.00  0.034  0.006    4.25     8.50 

*Leetonia,    Mesaba.  .  .54.34    2.41    0.62    0.09    0.04    0.57  0.054  0.004    6.1311.60 

*Sparta,    Mesaba 55.76    7.49    0.81    0.15    0.12    0.47  0.024  0.009    2.05     9.00 

*  Vivian,    Mesaba 38.6035.39    1.42    1.84    0.95    0.12  0.014  0.012    1.54     3.50 

t ,  Clinton,  N.   Y. 44.10  12.63    5.45      0.650  0.230      ...      2.77 

JSoft  ores,  •Alabama.. 47.2 1  17.20    3.35    1.12      7.00 

i Hard  ores,  Alabama. 37. 00  13.44    3.1816.20      0.370  0.07012.24     0.50 

Limonitcs. 

J ,  Alabama 48.5411.22    3.61     0.84      0.380  0.090    6.00     7.00 

JOriskany,    Virginia. ..44. 70  13.00    2.50      1.50  0.160  0.030      ...      8.00 

fRoanoke,    Virginia..  .40.80 16.60    4.20      2.30  0.50          7.00 

t ,   New  York 46.4514.10    3.05      0.370        

j ,   Staten   Island. 39.72  14.19    3.59      0.059  0.391      :..    12.41 

jJuniata,   Penna 43.4018.70    5.40    0.50    0.70    0.31  0.390  0.056      ...    10.37 


Materials  of  Manufacture.  69 


Magnetites. 

tChateaugay,    N.    Y. \49.24  18.48      0.029    0.052 

tChateaugay,  cone 66.00      0.003 

jMineville,  New  York.. .02. 10      1.108 

tHibarnia,  New  Jersey.53.75      0.3G4 

§  Cornwall,  Pa 45.8614.67    2.29    2.88    6.37    0.54  0.022    2.20 

§      Ditto,        ronstcd.  .47.10  16.05    4.73    3.60    6.80      ...  0.011    0.90 

fCranberry,   N.    C 64.64     • 0.004    0.115 

jCaluraet,    Colorado.  .49.23    3.85      0.026 

Foreign   Ores. 


fPoriran     Spain 

48  95 

14.04 

1.31 

0.74 

0.24 

0.85 

0.041 

0.271 

12.53 

3.55 

jfBedar     Spain 

52  43 

4.22 

0.73 

2.87 

0.62 

1.71 

0.022 

0.056 

7.60 

9.30 

IBilbao,     Spain  

.51.83 

11.  7G 

1.70 

0.45 

0.14 

0.84 

0.048 

0.025 

4.65 

§Calaspam,  Spain.  .  . 

.61.30 

4.25 

1 

.61 

1.88 

2.42 

0.19 

0.149 

0.060 

fJuragua,   Cuba..  .  .  . 

.  53.87 

13.95 

2 

.19 

3.10 

1.36 

0.24 

0.025 

0.237 

0.99 

§  Spanish-American, 

Cuba    

.62.85 

7.66 

0 

.58 

0.51 

0.45 

0.15 

0.028 

0.147 

0.95 

TIO, 

—  ,     Newfoundland 

.47.82 

0.86 

6.35 

0.11 

0.07 

0.33 

0.005 

0.014 

25.10 

SWabana.        Ditto.. 

.53.20 

13.00 

4.30 

1.80 

0.50 

0.30 

0.70 

0.170 

Scale  and  Cinders.  Cu. 

§BlueBilly,  N.  J 62.89    2.11      0.008  0.121     0.06       ... 

§  Roll  scale,  East.  Pa.  71. 36    2.48    0.08      ...      ...     0.38  0.125        2.06 

§Heating  cinder.  Ditto  52.30  25. 00    2.PO    p.25    0.0150.30  0.08  

§Puddlc  cinder.  .Ditto  50.75  19.88      1.19  1.57  0.14        ...      0.91 

*  From  published  analyses  of  Lake  Superior  Iron  Ore  Association,  1904. 

t  From  Kemp's  "  Ore  Deposits." 

j  Phillips,   "  Iron  Making  in  Alabama." 

§  Private  notes. 

FUEL. 

The  prime  object  of  the  use  of  fuel  in  a  blast  furnace  is  the 
production  of  heat.  At  the  same  time  it  acts  as  a  reducing  agent, 
separating  the  iron  from  its  oxygen.  Since  the  fuel  needed  to 
furnish  the  required  heat  is  always  in  excess  of  the  requirements 
for  reduction,  it  is  only  as  a  producer  of  heat  that  it  demands  con- 
sideration. 

The  materials  in  the  hearth  of  a  blast  furnace,  as  in  any  other 
form  of  melting  furnace,  will  melt  at  a  rate  proportionate  to  the 
rate  of  heat  development.  The  development  of  heat  will  be  in  pro- 
portion to  the  rate  of  union  between  the  carbon  of  the  fuel  and  the 
oxygen  of  the  blast.  Therefore  any  factor  which  tends  to  facili- 
tate this  union  will  increase  the  rapidity  of  operation.  One  of  the 
most  potent  factors  is  the  character  of  the  fuel.  Any  fuel  which 
tends  to  impede  the  movement  of  the  gases  or  which  is  not  easily 
attacked  by  the  blast  should  be  avoided. 


7Q  Blast  Furnace. 

The  characteristics  which  make  a  fuel  desirable  for  use  in  a 
blast  furnace  are  as  follows: 

A  Well-Developed  Cell-Structure. — A  porous  fuel  will  present 
more  surface  to  the  action  of  the  blast  than  a  dense  one,  and 
therefore  facilitates  and  hastens  combustion. 

Firmness. — A  fuel  which  changes  its  shape  in  the  furnace, 
either  through  being  crushed  by  the  weight  of  accompanying 
materials  or  through  softening  under  the  action  of  heat,  is  unde- 
sirable, as  the  rilling  of  the  interstices  of  the  charge  with  fine  or 
pasty  material  impedes  the  current  of  gases  and  hampers  combus- 
tion. 

Purity. — Other  conditions  being  equal,  it  is  evident  that  the 
higher  the  fixed  carbon  the  more  efficient  the  fuel.  The  non- 
carbonaceous  material  develops  no  heat,  but  forms  a  slag  which 
absorbs  heat  in  melting.  It  is  in  the  non-carbonaceous  material 
or  ash,  also,  that  is  found  the  phosphorus  which  is  so  dele- 
terious to  pig  irons. 

CONSTITUTION   OF   FUELS. 

Solid  fuel  consists  essentially  of  two  parts : 

(1)  The  combustible  portion,  consisting  of  carbon  and  hydro- 
carbons that  can  unite  with  oxygen,  thus  developing  heat  and 
passing  away  as  invisible  gases. 

(2)  The   incombustible  portion,   which   does   not   unite   with 
oxygen  and  is  left  behind  as  a  solid  residue,  commonly  called  ash. 
This  portion  consists  of  earthy  compounds  which  are  often  diffi- 
cult to  fuse  and  have  to  be  fluxed  from  the  furnace. 

Up  to  the  present  time  only  solid  fuels  have  been  used  success- 
fully in  the  blast  furnace.  Those  which  have  been  proved  suit- 
able are  of  three  general  types,  namely,  charcoal,  raw  coal  and 
coke.  Of  these  three  only  one,  raw  coal,  is  a  natural  fuel.  The 
other  two  are  produced  from  natural  fuels,  and  are  designed 
especially  for  use  in  the  blast  furnace.  Charcoal  is  obtained 
by  Distilling  the  volatile  matter  from  wood,  thus  leaving  behind 
only  the  solid  carbon.  Coke  is  produced  from  bituminous  coal 
by  a  similar  operation. 

Characteristics    of    Blast    Furnace   Fuels. — Each   of  the 


Materials  of  Manufacture.  71 

three  types  of  fuel  is  desirable  from  the  standpoint  of  some  one 
of  the  ahove  requirements. 

1 i )  From  the   standpoint  of    cell-structure,    porosity    and 
general  accessibility  to  the  blast,  anthracite  coal  is  the  least  de- 
sirable of  the  three.     It  is  a  dense  substance  which  offers  com- 
paratively little  surface  to  the  action  of  the  blast,  and  in  conse- 
quence burns   slowly.      Coke,   being  made  by  the   expulsion   of 
volatile  constituents,  is  naturally  more  porous  than  anthracite.     It 
offers  considerably  more  surface  to  the  action  of  the  blast,  and 
its  rate  of  combustion  is  two  to  two  and  a  half  times  that  of 
anthracite.     Charcoal  is  even  more  porous  than  coke.     It  presents 
three  times  as  great  an  area  for  contact  with  the  blast.     The 
calorific  effect  of  a  unit  of  fuel  in  a  unit  of  time  depends  upon 
three  factors,   (i)  the  area  of  fuel  exposed  to  the  action  of  the 
oxygen,  (2)  the  affinity  of  oxygen  for  the  given  form  of  carbon, 
(3)   the  pressure  and  temperature  of  the  blast.      Since  for  any 
given  fuel  the  first  two  factors  are  fixed,  it  is  only  by  control  of 
the  third  that  increased  activity  can  be  obtained. 

(2)  From  the  standpoint  of  firmness  it  is  probable  that  char- 
coal is  the  least  desirable,  as  it  is  a  very  friable  substance  and 
does  not  resist  well  the  crushing  force  of  the  charges.     Soft  coal, 
as  produced  from  the  bituminous  beds  of  the  Pittsburgh  district,  is 
out  of  the  question  as  a  blast  furnace  fuel,  since  it  fuses  into  a 
pasty  semi-liquid  mass  at  moderate  temperatures.     The  anthra- 
cite coals  of  eastern  Pennsylvania,  however,  are  firm  and  strong 
and  do  not  soften  at  any  temperature.     On  the  other  hand,  they 
decrepitate  or  splinter  into  fine  particles  under  the  influence  of 
heat  and  thus  become  undesirable.     Strong,  well-made  coke,  such 
as  is  made  from  the  Pittsburgh  coal  seam,  is  able  to  stand  the 
crushing  effect  of  the  charges  in  the  highest  furnaces.     As  it  has 
already  had  a  baptism  of  fire  during  its  preparation,   it  is  not 
altered  by  the  lieat  of  the  furnace  and  retains  its  original  shape 
until  it  is  burned  by  the  blast  at  the  tuyeres.     Hence  it  is  most 
desirable  from  this  point  of  view. 

(3)  From  the  standpoint  of    purity    and  freedom  from  non- 
carbonaceous  matter,  charcoal  unquestionably  stands  first.     Since 
it  is  made  from  vegetable  growths,  mineral  matter  is  present  only 
in  small  quantities.     The  quantity  of  ash  is  small,  and,  in  conse- 


72  Blast  Furnace. 

quence,  there  is  little  phosphorus.  Next  in  order  of  purity  is  an- 
thracite coal.  When  clean  and  well-picked,  it  is  very  high  in  car- 
bon and  reasonably  low  in  ash.  Its  content  of  phosphorus  and  sul- 
phur is  also  generally  fairly  low.  With  coke,  the  ash,  and  in  con- 
sequence the  phosphorus  and  sulphur,  is  likely  to  be  higher  than 
in  anthracite  and  much  higher  than  in  charcoal.  Coke  will  be 
much  higher  in  ash  than  the  coal  from  which  it  is  made.  This  is 
because  a  ton  of  coal  is  condensed  during  coking  into  about  two- 
thirds  of  a  ton  of  coke.  Since  the  ash  is  not  volatile,  but  remains 
with  the  coke,  the  ash  of  a  ton  of  coal  is  concentrated  into  two- 
thirds  of  a  ton  of  coke  and  consequently  appears  by  analysis  to 
be  50  per  cent,  higher  in  the  coke  than  m  the  coal.  According  to 
Tr.A.  i.  M.  E.,  McCreath,  the  phosphorus  in  Pittsburgh  coal  varies  from  a  trace 
to  0.125  per  cent.,  while  that  of  the  coke  varies  from  a  trace  to 
0.200  per  cent.  In  discussing  the  purity  of  fuels,  Birkinbine  gives 
as  illustration  the  following  comparative  averages: 

Per  cent.  P. 

OUr'  V&fSS    Charcoal 0.011 

Workers,     Anthracite    coal 0.018 

III.,  p.  361.     Coke    0  029 

It  is  evident,  therefore,  that  a  fuel  low  in  ash  is  of  double  advan- 
tage, for  while  it  is  lower  in  impurities,  it  likewise  needs  less  flux 
to  render  the  ash  fusible. 

In  summing  up  the  advantages  of  the  various  types  of  blast 
furnace  fuel,  we  are  led  irresistibly  to  the  conclusion  that  char- 
coal is  the  most  desirable,  coke  is  next,  and  anthracite  the  poorest 
form.  Yet  all  are  in  daily  use  in  various  parts  of  the  country, 
the  determining  factor  in  each  case  being  cost  alone. 

In  the  early  days  of  iron-smelting,  charcoal  was  the  only  suit- 
able fuel  known.  Wood  was  abundant,  and  the  demand  for  iron 
was  small.  It  was  easy  to  obtain  a  supply  of  charcoal  sufficient 
for  all  needs.  Each  locality  furnished  its  own  fuel,  and  the  small 
local  deposits  of  ore  served  as  an  ore  supply  adequate  to  the  needs 
of  the  times.  Every  state  was  then  a  producer  of  iron.  As  the 
demand  for  iron  increased,  and  charcoal  became  more  scarce,  a 
new  form  of  fuel  became  imperative.  About  the  third  decade  of 
the  last  century  it  was  found  that  iron  ore  could  be  smelted  in  the 
blast  furnace  with  anthracite  coal  as  fuel.  This  fact  gave  great 


Materials  of  Manufacture.  73 

impetus  to  the  iron  industry  in  eastern  Pennsylvania  and  vicinity, 
owing  to  its  proximity  to  the  supply  of  anthracite.  Improvements 
in  transportation  facilities  enabled  this  cheaper  product  to  kill  the 
local  industry  in  districts  remote  from  the  coal  supply. 

The  discovery  of  vast  beds  of  coking  coal  in  western  Penn- 
sylvania made  practicable  another  fuel,  which,  if  not  cheaper  than 
anthracite,  is  more  efficient.  This  discovery  enabled  the  iron  in- 
dustry of  that  locality  to  become,  during  the  last  quarter  of  the 
last  century,  the  greatest  in  the  world.  With  improved  transpor- 
tation this  more  efficient  fuel  has  invaded  even  the  home  of  the 
anthracite  iron  industry.  There  are  now  few  furnaces  in  the 
eastern  district  that  do  not  use  more  coke  than  anthracite  in  their 
charges,  and  many  have  abandoned  the  use  of  anthracite  entirely. 
The  use  of  a  given  fuel  is  determined  by  local  conditions.  In  the 
forest  districts  of  the  northwest,  which  are  remote  from  coking 
coals,  charcoal  is  still  used  for  smelting  iron  on  a  small  scale.  In 
the  vicinity  of  the  anthracite  coal  regions — also  remote  from  cok- 
ing coals — varying  proportions  of  anthracite  are  used  to  counter- 
balance the  high  cost  of  the  distant  coke.  In  the  great  region 
between,  however,  coke  is  the  universal  blast  furnace  fuel.  It 
may  be  safely  said  that  it  is  used  in  90  per  cent,  of  the  pig  iron 
production  of  the  United  States. 

NATURAL    FUELS. 

Anthracite  coal  is  a  natural  blast-furnace  fuel,  as  it  possesses 
properties  which  enable  it  to  be  used  successfully  without  prepara- 
tion. Such  use  is  confined,  however,  to  the  larger  sizes,  which 
range  from  fist  to  head  size. 

Geologically,  anthracite  appears  to  be  the  ultimate  product  of 
the  conversion  of  vegetable  matter  into  coal.  It  contains  very 
little  volatile  matter.  The  fixed  carbon  usually  amounts  to  at 
least  90  per  cent.  It  is  a  very  compact  black  substance,  having  a 
brilliant  sub-metallic  luster.  It  is  brittle,  having  an  uneven  con- 
choidal  fracture,  and  does  not  soil  the  fingers.  It  is  difficult  to 
ignite  and  burns  with  a  feebly  luminous,  smokeless  flame.  It 
decrepitates  on  heating  and  breaks  up  into  a  state  of  fine  division. 

Dry  bituminous  coals  are  used  for  smelting  in  some  coun- 
tries, but  have  no  application  in  this  country. 


74  Blast  Furnace. 

PREPARED   Ft' ELS* 

Coke  and  charcoal  are  fuels  prepared  from  soft  coal  and  wood 
respectively.  The  process  consists,  in  both  cases,  of  heating,  out 
of  contact  with  air,  to  such  a  temperature  that  the  volatile  matter 
is  expelled  without  the  combustion  of  the  solid  carbon.  The  solid 
carbon,  together  with  the  mineral  matter  comprising  the  ash,  con- 
stitutes the  blast  furnace  fuel. 

Formerly  this  distillation  was  accomplished  in  heaps  in  the 
open  air.  Later  crude  kilns  or  ovens  were  used,  from  which  the 
volatile  matter  escaped  into  the  air  and  was  lost.  Recently  great 
progress  has  been  made  in  methods  for  recovering-  the  various 
constituents  of  the  volatile  gases  as  by-products  of  considerable 
value. 

Coke — Coke  is  the  solid  residue  resulting  from  the  distilla- 
tion of  bituminous  coal.  Its  manufacture  is  of  comparatively  recent 
date.  It  was  first  called  into  use  in  England  by  the  increasing 
scarcity  of  charcoal  during  the  eighteenth  century,  and  had  prac- 
tically replaced  charcoal  there  before  the  American  Revolution. 

Coke  varies  much  in  appearance,  according  to  the  coal  from 
which  it  is  produced  and  the  manner  of  production.  Good  coke 
is  of  gray  color  and  porous,  yet  hard  and  resisting.  The  quality  is 
greatly  affected  by  the  temperature  and  duration  of  the  process. 
In  general,  the  higher  the  temperature  and  the  longer  the  ex- 
posure the  harder  the  coke. 

Coke  can  be  produced  only  from  what  are  known  as  "  coking  " 
coals.  Coking  is  not  a  universal  property  even  of  bituminous 
coals.  A  coking  coal  when  heated  to  certain  temperatures  will  swell, 
become  pasty  and  emit  bubbles  of  combustible  gas,  which  leave 
behind  them  a  solid,  coherent  mass  of  carbon.  The  result  is  the 
same  whether  the  coal  is  in  lump  or  powdered  form.  Coking  does 
not  take  place  at  temperatures  below  that  at  which  the  coal  under- 
goes decomposition.  It  is  not  the  result,  therefore,  of  simple 
fusion,  but  of  chemical  change.  The  degree  to  which  coking  may 
go  in  different  coals  ranges  from  complete  fusion  to  mere  fritting, 
and  the  line  between  coking  and  non-coking  coals  is  not  sharply 
defined.  Indeed,  mixing  a  portion  of  non-coking  coal  with  highly 
fusible  coal  may  result  in  perfectly  satisfactory  coke.  The  prop- 


Materials  of  Manufacture. 


75 


erty  of  coking  is  not  clearly  understood.  It  does  not  appear  to 
depend  upon  the  composition  of  the  coal.  It  may  be  destroyed 
entirely  by  prolonged  exposure  to  air  or  to  slightly  elevated  tem- 
peratures. 

Coking — The  process  of  coking  consists  essentially  of  driv- 
ing off  at  a  high  temperature  all  the  volatile  constituents  of  the  coal. 
The  volatile  matter  consists  chiefly  of  hydrocarbon  gases.  The 
solid  residue  contains  the  non-volatile  or  "fixed"  carbon,  to- 
gether with  the  ash,  the  phosphorus  and  most  of  the  sulphur.  As 
the  coke  is  usually  about  two-thirds  the  weight  of  the  coal  used,  it 
follows  that  all  residual  constituents  will  be  higher  in  the  coke. 
The  following  table  illustrates  the  change  due  to  distilling  some 
standard  coals: 


Locality. 
Connellsville    .  . 
Connellsvillc    Coke 


Substance.  Moisture.  Volatile.  Fixed  car. 
..Coal  1.25  31.27 


0.0.3 


1.37 


Connellsville    Coal 

Connellsville    Coke 

Davis    Coal 

Davis    Coke 

Thomas    Coal 

Thomas    .  .  .  Coke 


20.02 
1.85 

23.72 
1.12 

25.42 
1.20 


xed  car. 
59.79 
85.99 

Ash.       Sulphur. 
7.16           0.53 
11.12            0.89 

61.61 
87.07 

9.37 
11.08 

0.77 
0.75 

63.57 

88.  GO 

7.91 
10.28 

0.737 
0.669 

63.40 
85.45 

11,18 
13.35 

0.672 
0.665 

Although  by-product  coking  plants  are  springing  up  in  various 
sections  and  the  quantity  of  by-product  coke  in  use  is  constantly 
increasing,  the  bulk  of  the  coke  used  in  blast  furnaces  is  still 
made  in  beehive  ovens  without  the  recovery  of  by-products.  This 
great  daily  waste  of  valuable  material  is  due  chiefly  to  the  fact 
that  in  order  to  make  recovery  profitable  the  coking  plant  should 
be  located  near  a  large  city  or  industrial  establishment.  At  present 
much  capital  is  invested  in  beehive  ovens  located  at  coal  mines,  re- 
mote from  points  of  consumption. 

Beehive  Coke. — The  beehive  oven,  as  its  name  implies,  is  a 
dome-shaped  affair,  built  of  bricks  and  having  a  circular  ground 
plan.  It  is  usually  about  12  feet  in  diameter  and  6  feet  9  inches 
high,  ,vith  a  door  2^/2  feet  square  in  front  and  an  opening  about 
15  inches  in  diameter  in  the  crown.  The  charge  of  raw  coal,  con- 
sisting of  .about  5  tons,  is  dropped  into  the  oven  through  the 
opening  in  the  crown.  The  charge  is  leveled  and  the' door  bricked 


76 


Blast  Furnace. 


up  to  within  an  inch  of  the  top.     This  space  is  left  as  an  inlet  for 
air. 

As  the  oven  is  still  hot  from  the  previous  charge  some  of  the 
volatile  gases  begin  to  distill  at  once.  Then,  as  the  mass  gathers 
heat  from  the  brickwork,  the  temperature  rises  above  the  ignition 
point  of  the  gases  and  they  begin  to  burn  in  the  space  above  the 
charge.  The  air  to  support  their  combustion  enters  the  slit  in 
the  door,  and  the  products  of  combustion  pass  out  of  the  opening 
in  the  crown.  The  burning  gases  raise  the  temperature  of  the 


HE.GHT  OF  COKE  AT  BEST  31  1    INCHES 
HEIGHT  OF  COAL  CHARGED  23  INCHES 
HE.GHT  OF  COKE  AFTER  WATER.NG  21   INCHES 


Section  of  Beehive  Coke  Oven. 


oven,  and  the  distillation  continues  progressively  from  top  to 
bottom  of  the  coal.  At  the  temperature  of  the  oven  the  coal  fuses 
into  a  pasty  mass.  During  distillation  it  increases  in  volume,  ris- 
ing several  inches  in  the  oven.  The  maximum  swelling  occurs 
about  3^  hours  after  ignition.  As  the  volatile  matter  escapes, 
leaving  only  the  carbon  behind,  the  mass  again  becomes  solid  and 
shrinks  20  to  25  per  cent.  The  air  admitted  during  coking  should 
not  exceed  the  amount  needed  to  consume  the  gases,  as  any  excess 
will  attack  the  solid  carbon  and  cause  a  low  yield  of  coke.  The 


Materials  of  Manufacture.  77 

time  consumed  in  making  furnace  coke  is  usually  48  hours.  The 
charge  is  5  net  tons  and  lies  23  inches  deep.  For  making  better 
grades,  such  as  foundry  coke,  72  hours  is  allowed.  The  charge 
is  6  tons  and  27  inches  deep.  When  the  distillation  is  complete, 
the  door  is  torn  down  and  the  hot  coke  is  partly  cooled  by  a 
stream  of  water.  This  causes  the  mass  to  contract  and  split  up 
up  all  directions.  It  is  then  drawn  out  through  the  door  and 
further  cooled  by  water.  The  oven  is  then  ready  for  another 
charge. 

Coke  made  in  this  way  shows  a  distinct  columnar  structure. 
The  columns  are  about  eighteen  inches  long,  and  represent  the 
depth  of  the  mass  of  coke.  The  main  body  of  the  columns  is  com- 
pact, showing  a  silvery  white  luster,  with  here  and  there  clusters 
of  brightly  polished  nodules  and  filaments.  These  are  carbon 
which  has  been  deposited  by  the  decomposition  of  hydrocarbon 
gases  during  the  period  of  distillation.  The  lower  ends  of  the 
coke  which  come  in  contact  with  the  floor  of  the  oven  do  not 
receive  such  high  temperatures  as  the  upper  portions  and  are 
usually  darker  in  color  and  softer  in  texture.  These  "  black 
ends/'  as  they  are  called,  are  said  to  offer  less  resistance  to  abra- 
sion. Being  readily  dissolved  also  by  the  carbon  dioxide  of  the 
gases  in  the  top  of  the  furnace,  they  are  probably  carried  away 
before  they  have  served  any  useful  purpose. 

By-product  Coke. — Coke  made  in  retort  ovens  with  a  sav- 
ing of  by-products  is  being  rapidly  introduced  for  use  in  blast  fur- 
naces and  foundry  cupolas.  This  method  of  coking  differs  from 
the  beehive  method  in  that  the  operation  is  carried  on  in  closed 
retorts  so  that  the  gases  may  not  burn,  but  be  saved  for  future 
use.  Since  the  distillation  begins  at  the  retort  walls,  and  pro- 
gresses toward  the  middle  of  the  mass  of  coal,  it  follows  that  each 
side  distills  a  thickness  of  only  half  the  width  of  the  retort,  which 
is  nine  inches.  As  a  result  the  operation  takes  less  than  30  hours, 
as  compared  with  48  for  beehive  ovens.  However,  since  the  gas 
escapes  at  the  median  plane  of  the  mass,  a  plane  of  cleavage  is 
left,  and  the  resulting  coke  is  only  nine  inches  in  length.  Its 
small  size  and  lack  of  luster  make  it  appear  less  desirable  than 
beehive  coke.  Direct  comparison  of  the  two,  however,  in  the 
same  furnace  under  similar  conditions  shows  that  retort  coke  is 


Y8  tflast  Furnace. 

capable  01  carrying  a  heavier  burden,  and  of  producing-  more  iron 
of  a  given  quality  with  less  stone,  less  fuel,  and  lower  blast  tem- 
perature, owing  to  its  higher  percentage  of  fixed  carbon. 

Duration 

Poimcla     Pounds   Limestone,  I'.lnst  tern-  Output,  test, 

juneT"  1903',     Kind  of  coke.        ore.  fuel.          pounds,      erature.      tons.          Si.  S.       days. 

p>3!!-     P.eehive 11,310          1,885          2,  250          3,014          228          1.10          0.035          4 

Otto 11,575          1,787          2,050  924          233          1.06          0.039          4 

Retort  Ovens There  are  several  different  types  of  retort 

coke  ovens.  The  three  which  have  been  introduced  into  this  coun- 
try are  the  Otto-Hoffman,  the  Semet-Solvay  and  the  Koppcrs. 
The  difference  between  them  lies  chiefly  in  the  details  of  con- 
struction, such  as  the  arrangement  of  the  heating  flues,  and  in  the 
preheating  of  .  the  gas  and  air  used  in  the  flues.  They  are 
charged  by  overhead  larries  and  chutes,  and  discharged  by  a 
mechanical  pusher,  which  forces  the  retortful  of  coke  out  of  the 
retort  bodily.  The  water  cooling  then  takes  places  outside  of  the 
ovens,  and  there  is  no  corresponding  loss  of  heat. 

The  Otto-Hoffman  by-product  coke  retorts  were  first  intro- 
duced by  Otto  in  1881.  In  1883  Hoffman  added  regenerators  for 
preheating  the  air  used  in  the  combustion  of  the  heating  gas. 
The  retorts  are  built  of  firebrick  in  batteries  of  about  50.  Each 
retort  is  about  33  feet  long,  6  feet  high  and  16  to  24  inches  wide, 
and  is  closed  at  each  end  by  airtight  doors.  The  intervening 
walls  are  12  inches  thick  and  contain  flues  for  distributing  the 
heat  which  performs  the  distillation.  The  covering  arch  has 

2nd  Ed.,  p.  237. 

three  openings  for  charging  coal  and  two  others  for  conducting 
away  the  products  of  distillation.  The  latter  pass  into  the  col- 
lecting pipe  leading  to  the  condensing  plant,  where  they  are 
relieved  of  their  tar,  ammonia,  etc.  A  portion,  usually  one-half, 
of  the  purified  gas  is  then  returned  to  the  supply  pipe  of  the 
ovens  to  be  distributed  and  burned  in  the  flues  around  the  retorts. 
The  air  for  burning  the  gases  is  heated  in  the  regenerators  to  2,000 
degrees  F.  The  products  of  combustion  pass  up  the  vertical  flues, 
along  the  horizontal,  and  down  to  the  opposite  checkers,  thence 
to  the  chimney.  By  means  of  a  reversing  valve,  the  course  of  the 
gases  is  reversed  at  stated  intervals,  A  7  ton  charge  is  treated  in 


Materials  of  Manufacture. 


79 


24  to  36  hours.  The  yield  per  net  ton  of  Pittsburgh  coal  is  ap- 
proximately as  follows:  Coke,  1,300  pounds;  gas,  5,000  cubic 
feet ;  tar,  75  pounds ;  ammonic  sulphate,  20  pounds. 


The  Semet-Solvay  Retorts  were  introduced  in  1887.  They 
also  are  built  in  batteries.  The  retorts  are  slightly  smaller  than 
the  Otto,  however,  and  are  not  provided  with  regenerators.  They 
are  30  feet  long,  5^/2  feet  high,  and  i6y2  inches  wide.  They  have 


80 


Blast  Furnace. 


, 


three  openings  for  the  charging  of  coal  and  one  for  the  exit  of 
gas.  The  sides  of  each  retort  are  composed  of  jointed  horizontal 
flue  tiles,  having  walls  2^/4  inches  thick.  The  brick  wall  between 
two  adjacent  retorts  is  16  inches  thick,  exclusive  of  the  flue  tiles. 
These  thick  walls  serve  to  store  up  heat  toward  the  end  of  the 
period,  when  the  charge  is  hot,  and  to  give  it  out  when  a  cold 
charge  is  introduced.  This  makes  regenerators  unnecessary,  and 


Semet-Solvay  By-Product  Coke  Oven. — Longitudinal  and  Cross  Sections. 

the  current  is  therefore  constantly  in  one  direction.  The  high 
initial  temperature  melts  the  fusible  constituents  at  the  start, 
thereby  making  stronger  coke.  This  type  of  retort  is  especially 
good  for  poorly  coking  coals.  A  charge  of  4^  tons  is  coked  in 
1 8  to  26  hours. 

Standard  Coke.  — Coals  from  different  beds  do  not  yield 
the  same  quality  of  coke  even  in  the  same  method  of  coking.  The 
Pittsburgh  vein  in  the  vicinity  of  Connellsville,  Pa.,  has  always 
yielded  coke  of  the  first  quality,  it  being  very  strong  and  hard,  with 


Materials  of  Manufacture.  81 

good  cell  structure  and  low  in  phosphorus.  It  is  a  little  higher 
in  ash  than  some  other  good  cokes,  but  its  other  qualities  have 
long  made  it  the  standard  of  comparison.  Its  closest  competitor 
for  general  favor  is  made  from  the  coals  of  the  Pocahontas  dis- 
trict in  West  Virginia.  It  is  inferior  to  the  Connellsville  coke 
in  physical  properties,  but  is  much  lower  in  ash  and  higher  in 
fixed  carbon. 

Impurities  in  Coal. — The  chief  impurities  in  coal,  consid- 
ered as  a  metallurgical  fuel,  are  sulphur  and  phosphorus.  Sulphur 
is  always  present  in  coal.  It  may  exist  in  combination  with  bases 
as  sulphates,  or  united  with  iron  as  pyrite,  but  is  principally  in 
combination  with  the  organic  constituents  of  the  coal.  The  pyrite 
may  exist  in  conspicuous  masses  or  it  may  be  disseminated 
through  the  coal  as  invisible  particles.  During  the  distillation  a 
portion  of  the  sulphur  is  evolved  as  sulphuretted  hydrogen,  or 
as  a  bisulphide  of  carbon.  The  proportion  thus  eliminated  ranges 
up  to  30  per  cent,  of  the  whole. 

The  phosphorus  occurs  combined  with  bases  as  phosphates, 
particularly  the  phosphate  of  lime,  or  apatite.  These  phosphates 
are  not  decomposed  during  distillation,  but  are  concentrated  with 
the  ash,  and  hence  represent  a  higher  percentage  of  the  coke  than 
of  the  coal.  Coals  which  are  high  in  mineral  ^natter  such  as 
slate,  pyrite,  etc.,  are  sometimes  washed  before  coking.  They  are 
crushed  to  meal  sizes,  and  jigged,  whereby  the  quantity  of  ash 
is  lessened  and  distributed  more  evenly,  thus  making  a  stronger 
coke. 

Statistics. — The  first  by-product  coke  ovens  in  the  United 
States  were  put  into  operation  in  Syracuse,  New  York,  in  1893. 
Since  then,  the  number  has  increased  rapidly.  They  are  not  con- 
fined to  the  coal-producing  or  smelting  districts,  but  ;are  being 
established  in  manufacturing  communities,  where  there  is  demand 
for  gaseous  as  well  as  solid  fuel.  The  comparative  output  for 
the  last  few  years  is  as  follows : 

1905.  1906.  1907.  1908. 

Number   ovens   existing 8,159  3,603  3,892  4,007 

Coke  produced,  net   tons 3,462,348  4,558,127  5,607,899  4,201,226 

Average  product  per  oven,  net  tons..         1,159  1,356  1,472  1,142 

Per  cent,  total  coke  production 10.7  12.6  13.7  16.1 

Total  coal   used,  net  tons 4,628,981  6,192,086  7,506.174  5,699,058 

Average  yield,   per  cent 75  73.6  75.0  73.7 


82 


Blast  Furnace. 


Jour.  U.  S.  Ass'n 

Charcoal  Iron 

Workers, 

V.,  p.  3:!. 


Coke  is  made  in  all  of  the  seven  bituminous  coal  fields  of  the 
United  States.  By  far  the  greatest  amount  comes  from  the  Ap- 
palachian district,  which  includes  such  important  iron-producing 
states  as  Pennsylvania,  Ohio,  Virginia,  West  Virginia,  Ken- 
tucky, Tennessee,  Georgia  and  Alabama. 

Charcoal — When  wood  is  heated  without  contact  of  air,  it 
breaks  up  into  certain  volatile  products  and  a  fixed  carbonaceous 
residue  known  as  charcoal.  The  charcoal  retains  the  structure  of 
the  original  wood,  is  black  in  color,  very  light  and  extremely 
porous.  Good  charcoal  gives  a  sonorous  ring  when  struck,  and 
while  it  breaks  easily,  is  not  readily  crushed  by  ordinary  pressure. 
When  ignited  it  burns  without  flame. 

While  charcoal  retains  almost  the  bulk  of  the  original  wood, 
its  specific  gravity  is  very  low.  As  a  result  the  average  yield  of 
charcoal  is  20  to  25  per  cent,  of  the  wood.  Of  this  the  ash  rarely 
averages  over  about  3  per  cent.  Charcoal  made  at  low  tempera- 
tures and  of  soft  wood  ignites  most  readily.  That  which  is 
burned  at  high  temperatures  ignites  with  difficulty. 

Charcoal  Making. — Charcoal,  which  was  formerly  burned  in 
heaps  or  kilns  without  recovery  of  the  by-products,  is  now  usually 
made  in  retorts  with  recovery.  It  is  made  from  various  kinds 
of  wood,  and  ift  properties  vary  accordingly.  Its  weight  varies 
widely  from  23.5  pounds  per  bushel  when  made  from  black  oak, 
to  14  pounds  per  bushel  when  made  from  alder.  A  bushel  of 
mixed  charcoal  weighs  usually  about  20  pounds.  It  is  convenient 
to  assume  that  100  bushels  make  a  net  ton.  The  following  are 
some  average  analyses  of  charcoal  made  from  different  kinds  of 
wood : 

Fixed 

carbon. 
Kind  of  wood.  Per  cent. 

Pine    89.52 

Ash   89.10 

Spruce    87.25 

Birch    86.50 

Willow    80.04 

Fir    73.00 

Alder    Sl.r.O 

From  these  analyses  it  appears  that  during  the  distillation  the 
volatile  constituents  are  never  wholly  expelled ;  that  charcoal 


Volatile 

matter. 

Moisture. 

Ash. 

P. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

4.46 

5.15 

0.87 

0.014 

5.63 

4.03 

1.15 

6.08 

5.77 

0.92 

0.016 

7.17 

5.61 

0.65 

0.020 

4.23 

5.93 

3.80  ^ 

.... 

1  9.30 

5  5° 

]  .58 

8.40 

6.40 

3.70 

Materials  of  Manufacture.  83 

absorbs  moisture  amounting  usually  to  at  least  5  per  cent,  of  its 
weight  and  that  the  ash  and  phosphorus  are  both  very  low  as 
compared  with  coal  and  coke. 

The  average  analysis  of  wood  is  approximately  as  follows : 

Per  cent. 

Fixed  carbon 51.6 

Hydrogen    6.5     iron  Age, 

Osygen    41.8    *•?*""• 

Nitrogen 0.1 

It  is  apparent  that  under  the  most  favorable  conditions  there 
must  be  more  waste  and  less  recovery  in  making  charcoal  than  in 
making  coke,  since  the  volatile  constituents  are  in  larger  propor- 
tion. For  this  and  other  reasons  the  use  of  kilns  and  closed  re- 
torts was  early  adopted  in  charcoal  making. 

The  making  of  charcoal  in  retorts  at  the  Algoma  Steel  Com- 
pany plant  at  Sault  Ste.  Marie  is  conducted  as  follows:  The  re- 
torts consist  of  rectangular,  horizontal  shells  46  feet  long,  6^4 
feet  wide,  and  8^  feet  high,  made  of  ^j-inch  plates.  They  are  ironAgA. 
riveted  together  with  calked  seams,  and  fitted  at  the  ends  with 
doors,  which  are  capable  of  air-tight  sealing.  They  are  set  in 
brick  walls  like  a  boiler,  and  have  a  fireplace  at  each  end  with 
flues  leading  to  a  stack  so  arranged  as  to  heat  the  retorts  evenly. 
The  wood  is  split  and  seasoned,  then  loaded  on  trucks  and  run 
into  the  retort,  where  it  is  subjected  to  heat  for  24  hours,  18  or 
20  of  which  it  is  at  the  full  temperature  of  carbonization.  The 
distillation  products  are  led  to  the  by-product  plant  for  the  re- 
covery of  alcohol,  acetic  acid,  tar,  etc.,  and  the  gas  is  sent  to 
boilers  to  raise  steam.  After  the  distillation  is  complete,  the 
trucks  are  pushed  into  the  first  cooler.  The  coolers  are  duplicates 
of  the  retorts.  After  a  stay  of  24  hours,  the  trucks  pass  to  the 
second  cooler  for  24  hours,  when  the  charcoal  is  ready  for  the 
blast  furnace.  This  system  obviates  all  rehandling  of  materials, 
as  the  wood  is  not  touched  after  it  is  placed  on  the  trucks  until 
as  charcoal  it  is  charged  into  the  furnace. 

The  following  is  a  comparison  by  Sjostedt  of  the  value  of 
a  cord  of  wood  carbonized  under  different  systems : 


84 


Blast  Furnace. 


Ibid. 


Gallons 

Bushels       wood 
charcoal,    alcohol. 


In  metiers,  "  coaling  under  dust  "..33-3,") 

In  kilns  without  recovery  .......  43  45 

In  kilns  with  recovery  : 

Mixed    hardwood  ...........  43-45 

Southern  pine  .............  43-45 

In  retorts  : 

Mixed  hardwood  ...........  50-52 

Southern  pine  .............  50-54 


The  advantage  of  retorts  is  that  the  by-products  are  preserved 
uncontaminated,  and  cheap  fuel  may  be  used  for  distillation. 


8-12 


Pounds 

Gallons 

Value 

calcic 

spirits 

per 

acetate. 

turp. 

Tar. 

cord. 

0 

0 

0 

$2.04 

0 

0 

0 

2.64 

50-100 

3 

4.04 

50-75 

5 

5 

4.08 

150-200 

5 

7.65 

120 

10 

10 

7.37 

FUEL   CONSUMPTION    IN    THE    UNITED   STATES. 

Until  1855  the  chief  blast  furnace  fuel  in  America  was  char- 
coal. In  that  year  the  output  of  anthracite  pig  for  the  first  time 
exceeded  that  of  charcoal  pig.  In  1869  the  production  of  coke 
iron  first  exceeded  that  of  charcoal  iron,  and  in  1875  coke  also 
surpassed  anthracite  as  a  metallurgical  fuel. 

The  first  statistics  concerning  the  production  of  coke  date 
from  1883,  when  3,338,300  net  tons  were  made.  The  comparative 
production  for  the  past  three  years  in  the  United  States  was  as 
follows : 

1906. 

In   Pennsylvania,   net   tons 23,000,511 

In   Alabama,   net   tens 3,034,501 

In   West  Virginia,   not   tons 3.713,514 

In   Virginia,   net    tons 1,577,659 

In  other  States,  net  tons 5,015,032 

Total  in  United  States,  not  tons 36,401,217 

Total  coal  used,  net  tons 55,710.374 

Average   yield,    per   cent 65.3 

Number   ovens   existing 03,001 

Number    active 88,506 

Average  product  per  active  oven,  net  tons  410.9 

It  may  be  observed  that  in  1907  the  yield  of  beehive  ovens  was 
60.7  per  cent,  as  compared  with  75  per  cent,  for  the  by-product 
ovens. 


1907. 

1908. 

26,513,214 

15,511,634 

3,021,794 

2,362,666 

4,112,896 

2,637,123 

1,545,280 

1,162,051 

5,586,380 

4,360,044 

40,779,564 

20,033,518 

61,946,109 

39,440,837 

65.8 

66.0 

99,680 

101,218 

94,746 

88,298 

430.4 

294.8 

Materials  of  Manufacture.  85 

FUEL   ANALYSES. 

Volatile   Fixtcl 
HoO.  matter,  carbon.  Ash.       S.       P.       Si02  A12O3  Bases.  Fe. 

Connellsville.    Pa.,   coke 

(aver.  200  cars)... 0.32  1.70  86.50  11.50  0.75  0.020  5.30  3.00  4.30  2.60 
Pocahontas,  W.  Va., 

coke  (av.  405  cars).  2.31  90.62  6.97  0.70  

New  River,  W.  Va., 

coke  2.82  90.52  6.3G  0.70  

Davis,  W.  Va.,  coke..  .0.33  1.20  87.97  30.50  0.55  0.034  4.27  3.89  ...  1.40 

Derry,  Pa.,  coke 2.50  81.60  14.70  1.20  

Webster,  Pa.,  coke 1.10  88.40  10.50  0.95  0.03  4.80  3.50  ...  1.85 

Klondike,  Pa.,  coke 2.50  84.50  12.00  1.00  

Loyal  Hanna,  Pa.,  coke.  2.45  81.20  15.00  1.35  

Mountain,  Pa.,  coke..  .0.50  1.10  85.85  11.53  1.00  0.018  

Fairmont,  W.Va.,  coke.0.30  0.97  87.43  11.30  1.35  0.020  4.16  2.53  .  .  .  2.45 
Camden  by-product,  Otto 

Hoffman 0.40  1.20  84.60  13.80  0.88  0.039  5.70  4.59  ...  1.55 

Anthracite,  Pa 8.30  78.00  13.00  0.70  

VALUATION    OF    FUELS. 

Since  a  fuel  is  primarily  intended  to  furnish  heat,  it  is  evi- 
dent that  its  valuation  must  be  based  upon  the  available  units  of 
carbon  which  it  contains.  The  available  carbon  is  that  which  is 
left  after  deducting  from  the  fixed  carbon  the  amount  necessary 
to  melt  the  slag  formed  by  the  ash  and  sulphur  of  the  fuel  and 
the  stone  needed  to  flux  them.  In  order  to  estimate  the  approxi- 
mate amount  of  stone  needed,  it  is  convenient  and  sufficiently  ac- 
curate to  consider  that  the  ash  requires  double  its  weight  of 
stone,  and  the  sulphur  three  and  one-half  times  its  weight.  The 
weight  of  the  ash,  plus  the  weight  of  the  sulphur,  plus  the  weight 
of  the  slag- forming  portion  of  the  calculated  stone,  will  give  the 
weight  of  the  slag  formed  by  the  fuel.  If  the  slag  requires  25 
per  cent,  of  its  weight  of  carbon  to  melt  it,  then  25  per  cent,  of 
the  weight  of  slag  deducted  from  the  total  fixed  carbon  will 
leave  the  available  carbon.  For  example,  a  coke,  having  the 

following  analysis : 

Per  cent. 

Fixed    carbon 84.40 

Ash 12.00 

Sulphur 1.15 

will  require  (2  X  12)  +  (3.5  X  1.15)  =  28  per  cent,  stone. 
If  the  stone  contains  43  per  cent.  CO2  it  will  contribute  57  per 
cent,  to  the  slag.  Hence  the  weight  of  slag  per  100  pounds  fuel 


gg  Blast  Furnace. 

will  be  12  +  1.15  +  (28  X  -57)  zr  29-11  pounds.  29.11  X  .25 
—  7.28.  the  carbon  used  by  its  own  slag.  84.40  —  7.28  =  77.12, 
available  carbon. 

The  relative  powers  as  heat  producing  agents,  of  fuels,  and 
consequently  their  relative  values  to  a  furnace  man,  are  in  pro- 
portion to  their  respective  amounts  of  available  carbon.  To  find 
their  respective  cash  values,  it  is  only  necessary  to  estimate  their 
relative  costs,  based  on  the  amounts  of  available  carbon,  and  the 
price  paid  per  ton,  and  then  to  deduct  the  cost  of  the  stone  needed 
to  flux  the  ash  and  sulphur.  In  comparing  the  smelting  powers  of 
various  fuels,  the  only  safe  basis  of  comparison  is  that  of  the 
available  carbon. 

FLUXES. 

The  function  of  a  flux  is,  as  the  name  implies,  to  facilitate 
flow.  All  matter  which  is  infusible  or  fusible  with  difficulty  at 
furnace  temperatures  must  have  its  composition  so  modified  that 
the  fusibility  will  be  increased.  A  suitable  flux  cannot  be  se- 
lected without  a  knowledge  of  the  composition  of  the  material 
to  be  fluxed.  In  general  it  may  be  stated  that  if  the  matter  to  be 
fluxed  be  basic,  such  as  lime,  magnesia,  or  "similar  alkaline  mat- 
ter, the  flux  must  be  acid  in  nature,  such  as  silica,  alumina,  etc. 
On  the  other  hand,  acid  gangues,  such  as  silica,  alumina,  etc.,  re- 
quire basic  fluxes.  As  a  rule  gangues  are  acid  in  their  nature. 
The  acidity  may  be  partly  neutralized  by  the  presence  of  basic 
matter.  There  is  very  seldom  sufficient  basic  matter  to  completely 
neutralize  the  acid  components.  As  a  result,  we  find  that  fluxes 
are  almost  invariably  basic  in  character. 

Any  of  the  metallic  oxides  may  act  as  flux  for  silica  and  alumi- 
na, but  the  cheapest,  and  hence  the  one  most  generally  used,  is 
lime  (CaO).  The  lime  is  generally  introduced  into  the  furnace  in 
the  condition  of  calcic  carbonate  (CaCO3),  usually  in  the  form 
of  limestone,  though  sometimes  as  oyster  shells. 

When  the  limestone  which  has  been  charged  into  the  furnace 
has  descended  to  the  point  where  the  temperature  is  above  1100° 
F.,  it  begins  to  decompose  in  accordance  with  the  following  reac- 
tion: 

CaCO3  =  CaO  +  CO2. 
The  CaO  thus  liberated  continues  to  descend  with  the  charge 


Materials  of  Manufacture.  87 

until,  in  the  zone  of  fusion,  it  unites  with  the  gangue  to  form  the 
slag.  The  CO2,  however,  joins  the  current  of  gases  and  passes 
upward.  If  it  encounters  on  its  way  any  coke  which  is  at  suffi- 
ciently high  temperature,  it  will  attack  it  thus, 

CCX  +  C  =  2CO 

and  the  carbon  thus  dissolved  will  be  carried  out  of  the  furnace, 
without  having  developed  any  useful  heat.  It  would  appear  ad- 
vantageous, therefore,  to  decompose  the  limestone  before  charg- 
ing it,  since  only  the  CaO  is  needed  and  the  CO2  steals  coke. 
Experiments  indicate,  however,  that  the  advantages  of  using 
caustic  lime  instead  of  limestone  are  not  marked.  This  is  well 
shown  by  excerpts  from  experiments  by  Sir  Lowthian  Bell. 

Coke,     Weight  flux  Ore,     Iron,  tons.  Time, 

Furnace.       Flux.                     pounds.       pounds.  pounds,  per  week.  Grade,  weeks. 

No.  11.      Limestone 2. 182            1,176  4,722            451            3.3            19    Inst.  Jour., 

No.  11.      Lime    2;009               862  4,734            497            3.3            17    JJJfc  ^ 

No.  12.     Limestone 2,201"           1,187  4,762            459            3.3            19 

No.  12.      Lime    2,014               857  4,740            481            3.3            17 

From  the  above  it  appears  that  with  caustic  lime,  less  fuel  is 
needed  and  more  iron  is  made,  of  the  same  quality  from  the  same 
burden.  The  additional  cost  of  calcination,  however,  about  off- 
sets the  gain. 

Experiments  by  Cochrane  show  very  similar  results. 

Blast     Blast      Out-  CQ     Temp.     Wt. 

Lime,    Lime-     Fuel,       Ore,    temper-  press.,     put,  -  waste    waste 

Time.        pounds,  stone,  pounds,  pounds,  ature.  pound^tons.        2'  gases,    gases.    I"st-  Jour., 

6   months 0     1,391      2,122      7,238     1,474     5.04     3,534  1.77     607     125.62 

4    months 599         504     2,019     7,038     1,489     4.97     3,625  1.94     589     120.02 

On  half  lime  there  is  a  decrease  of  fuel  and  increase  of  output 
with  better  extraction  and  cooler  top.  The  benefits  which  would 
naturally  be  expected  from  the  use  of  caustic  lime  as  a  flux  are 
neutralized  by  its  tendency  to  absorb  CO2  from  the  escaping 
gases.  This  reaction  partly  undoes  the  results  of  calcination,  as 
CO2  is  absorbed  and  carried  down  with  the  charge,  only  to  be 
released  and  later  to  dissolve  some  of  the  coke,  thereby  decreas- 
ing the  expected  economy. 

The  limestone  is  charged  into  a  furnace  crushed  to  pass 
4  to  6  in.  rings.  By  the  time  it  has  reached  the  zone  of  fusion 


88  Blast  Furnace. 

it  has  been  practically  calcined,  and  only  the  CaO  remains. 
•'It  is  the  duty  of  the  CaO  to  unite  with  any  free  silica  and 
alumina  and  to  form  slag.  As  stated  above,  some  of  the  silica 
and  alumina  may  already  be  in  combination  with  an  equivalent  of 
bases  which  were  present  in  the  original  gangue  of  the  ore.  The 
lime  is  added  only  to  take  care  of  the  surplus  of  acids.  On  the 
other  hand,  few  limestones  are  so  pure  that  they  do  not  contain 
a  small  percentage  of  silica  and  alumina,  and  their  demand  for 
bases  must  be  satisfied  before  there  will  be  any  bases  available 
to  flux  the  gangue  and  ash.  As  the  amount  of  bases  in  the  slag 
of  a  blast  furnace  is  usually  about  equal  to  the  acids,  it  is  evident 
that  the  presence  of  acids  in  limestone  rapidly  decreases  its  effi- 
ciency, thus  making  it  imperative  that  pure  stone  be  used.  A 
suitable  stone  should  contain  at  least  95  per  cent,  pure  carbonate. 

In  addition  to  combining  with  the  silica  and  alumina,  the 
CaO  should  seize  and  carry  into  the  slag  as  much  as  possible  of 
the  sulphur.  Ten  per  cent,  of  the  sulphur  in  a  charge,  if  allowed 
to  enter  the  iron,  is  usually  enough  to  make  pig  iron  unsuitable 
for  most  purposes.  It  is  imperative,  therefore,  that  the  greater 
part  of  the  sulphur  should  be  removed.  This  duty  devolves  upon 
the  lime,  which  unites  with  the  sulphur,  forming  calcic  sulphide 
(CaS),  and  enters  the  slag. 

In  some  localities  pure  limestone  is  not  available  and  it  is 
necessary  to  resort  to  the  magnesian  variety,  which  is  called 
dolomite.  True  dolomite  contains  one  atom  of  magnesium  to 
every  one  of  calcium,  and  may  be  represented  by  the  symbol 
MgCa(CO3)2.  Not  all  magnesian  limestones  attain  to  the  full 
condition  of  dolomite.  The  proportion  of  magnesium  varies  from 
traces  to  equivalent  parts. 

The  presence  of  magnesium  in  small  quantities  makes  no  ap- 
preciable difference  in  the  behavior  of  the  flux.  When  asso- 
ciated with  calcium  in  considerable  proportion,  however,  it  tends 
to  make  the  slag  less  refractory  than  the  calcium  alone,  since 
double  silicates  are  more  fusible  than  silicates  of  a  single  base. 

It  has  been  claimed  by  some  that  magnesian  limestone  does 

not  hold  sulphur  in  the  slag  as  well  as  pure  limestone.     F.  Firm- 

J!'4&!   stone  states  that  the  substitution  of  dolomite  for  limestone  in  the 

furnace  at  Glendon,  Pa.,  made  the  sulphur  in  the  iron  lower  and 


Materials  of  Manufacture. 


89 


more  regular.     At  the  same  time  the  furnace  worked  better.     It 

is  stated  also  by  E.  A.  Uehling  that  the  substitution  of  dolomite    IronAgf> 

at  Birmingham,  Ala.,  for  the  limestone  up  to  three  fourths  of  th*e   July19.1894- 

total  gave  only  good  results.    The  sulphur  in  the  coke  was  above 

the  average,  yet  the  iron  was  of  good  quality  and  the  furnaces 

worked  better  than  on  limestone.     W.  B.  Phillips  states  that  in 

Alabama  "  the  use  of  dolomite  is  a  decided  advantage,  especially    "iron  Making 

,.  -  .        in  Alabama," 

in  the  elimination  of  sulphur.       it  is  not  apparent 'whether  this    Geoi.  sur. 
result  was  due  to  the  presence  of  magnesium  or  to  the  absence  of 
silica,   since  the  dolomite  was  exceptionally  pure,   as  shown  by 
the  following  analysis  of  the  limestone  and  dolomite. 

SiO2.  R3O3.  CaCO3.  MgCOa. 

Limestone    4.00  1.00  94.60  

Dolomite    1.50  1.00  54.00  43.00 

Relative  Values  of  Fluxes — The  relative  values  of  fluxes 
evidently  depend  upon  the  power  of  a  given  weight  to  flux  refrac- 
tory constituents.  This  quantity  is  manifestly  in  proportion  to 
the  quantity  of  available  bases  present  in  the  flux. 

The  Available  Base — By  the  available  base  of  a  flux  is 
meant  the  base  that  is  left  free  to  unite  with  the  gangue  and  ash. 
It  consists  of  that  portion  of  the  stone  which  remains  after  there 
has  been  deducted  the  CO2,  the  acid  impurities  and  the  portion  of 
the  base  which  is  necessary  to  flux  the  acid  constituents.  For 
example,  if  a  limestone  having  96.15  per  cent.  CaCO3  and  3.85 
per  cent,  acids,  were  to  be  used  as  a  flux  in  a  slag  having  acids 
equal  to  bases,  the  available  base  can  be  found  as  follows,  remem- 
bering that  CaO  is  56  per  cent,  of  CaCO3 : 

96.15  X  0.56  rz  53.85  =  total  base. 

3.85  =  base  needed  to  neutralize  acids. 

50.00  =  available  base. 

The  available  base  is  the  only  safe  basis  of  comparison  of  the 
relative  value  of  various  fluxes. 

ANALYSES   OF   FLUXES. 


Limestones  and  dolomites. 
Annville,  Pa  

Si02. 
.  .  .0.04 

R203. 
0  72 

CaCOs. 

96  78 

MgCO3. 
1  23 

S. 
0  012* 

P. 

0  004 

Wrights  ville    Pa 

1  44 

•>  12 

89  55 

13  50 

0  032 

0  020 

Maryland    

.  .  .0.78 

0.86 

97  48 

1  21 

Kelley  Island    Lake  Erie 

1  15 

1  04 

§9  41 

15  64 

Avondale,  Pa.  (white)  

.  .  .1.50 

1.36 

66  50 

30  40 

0  004 

0  005 

Avondale,  Pa.  (gray)  

.  .  .  3  94 

2  80 

59  51 

33  26 

0  132 

0  019 

Buena  Yista,  Va  

1.34 

0  92 

54  50 

Tr 

Buena  Vista.  Va  

0  75 

1  OS 

29  80 

21  °0 

.  .  • 

.  •  • 

Birmingham,  Ala..  . 

.  .1.75 

1.20 

31.70 

19.  OO 

CHAPTER    II. 
DESCRIPTION   OF  PLANT. 

Introductory — From  the  small  beginnings  of  a  century  ago, 
the  blast  furnace  plant  has  developed  into  a  gigantic  affair  with 
truly  formidable  equipment.  The  various  members  which  go 
to  make  up  such  a  plant  may  be  profitably  enumerated  before  pro- 
ceeding to  a  description  of  them. 

The  process  of  smelting  iron  in  the  blast  furnace  consists  es- 
sentially of  charging  a  mixture  of  fuel,  ore  and  flux  into  the  top 
of  the  furnace,  and  simultaneously  blowing  in  a  current  of  heated 
atmospheric  air  at  the  bottom.  The  air  burns  the  fuel,  forming 
heat  for  the  chemical  reactions,  and  for  melting  the  products ;  the 
gases  formed  by  this  combustion  remove  the  oxygen  from  the  ore, 
thereby  reducing  it  to  metallic  form ;  the  flux  renders  fluid  the 
earthy  materials.  The  gaseous  products  of  the  operation  pass  out 
of  the  top  of  the  furnace,  while  the  liquid  products,  cast  iron  and 
slag,  are  tapped  at  the  bottom.  The  escaping  gases  are  combus- 
tible, and  therefore  are  conducted  through  pipes  to  boilers  and 
stoves  where  they  perform  the  useful  services  of  heating  the  blast 
and  raising  steam  or  operating  internal  combustion  engines. 

It  is  evident,  therefore,  that  several  factors  enter  into  the 
composition  of  a  complete  smelting  unit.  The  central  feature  is 
the  furnace  with  its  hoists  and  skips  for  the  handling  of  charges, 
and  its  ladles  and  pig-machines  for  handling  the  products.  Quite 
as  essential  are  the  blowing  engines  which  drive  the  blast  to  the 
furnace,  and  the  series  of  hot  blast  stoves,  which  heat  the  -blast 
on  its  way.  Not  less  important  are  the  boiler  plants  which  furnish 
the  power  to  drive  the  blowing  engines,  the  gas  engines  operating 
electric  motors  or  blowing  engines,  and  the  pumps  which  supply 
the  vast  quantities  of  water  needed  for  cooling  purposes  and  for 
power  development. 

THE  FURNACE. 

A  blast  furnace  consists  essentially  of  an  enclosed  space  or 
shaft  for  reducing  and  melting  materials,  and  a  crucible  for  col- 

90 


Description  of  Plant. 


9.1 


lecting  the  molten  products  of  the  operation.  The  crucible  is 
cylindrical.  The  shaft  has  the  shape  of  two  conical  frustrums 
placed  base  to  base,  and  surmounts  the  crucible.  The  greatest 
width  of  shaft  will  evidently  be  at  some  point  between  the  cruci- 
ble and  the  top  of  the  shaft.  By  such  an  arrangement  the  pathway 
presented  to  the  materials  descending  the  shaft  constantly  grows 


View  of  Hearth  of  Blast  Furnace. 


larger,  thereby  facilitating  their  descent  while  they  are  solid.  The 
space  contracts  as  the  materials  approach  the  zone  of  fusion,  and 
the  converging  walls  furnish  support  for  the  lessening  bulk.  The 
crucible  serves  to  hold  the  liquid  iron  and  slag  until  the  accumula- 
tion is  sufficient  to  be  drawn  off. 

Such  in  brief  are  the  essential  features  of  the  furnace.  The 
crucible  is  more  often  termed  the  "  hearth."  The  point  of  great- 
est diameter  in  the  shaft  is  called  the  "  bosh."  The  region  en- 


92 


Blast  Furnace. 


closed  by  the  sloping  walls  which  connect  the  hearth  and  the  bosh 
is  termed  "  the  boshes "  of  the  furnace.  The  tapering-  walls 
reaching  upward  from  the  bosh  are  called  the  "  inwalls."  The  top 
of  the  furnace  is  closed  by  the  "  bell  and  hopper,"  which  rests  on 


View  of  Hot-Blast  Stove  Connections. 


the  top  of  the  inwalls.     The  portion  of  the  shaft  just  below  the 
hopper  is  called  the  "  stockline." 

Though  furnaces  are  built  in  many  sizes,  the  dimensions  of 
these  various  parts  are  generally  proportional.  The  maximum 
sizes  which  have  been  so  far  attempted  are  as  follows :  Total 


Description  of  Plant.  93 

height,  106  feet;  bosh  diameter,  24  feet;  hearth  diameter,  17  feet; 
stockline,  18  feet. 

FURNACE    CONSTRUCTION. 

From  the  point  of  view  of  construction,  the  blast  furnace  may 
be  looked  upon  as  being  made  up  of  a  steel  shell  and  a  brick 
lining.  The  shell  of  the  shaft  above  the  boshes  is  always  con- 
structed independently  of  the  shell  of  the  parts  below.  It  con- 
sists usually  of  steel  plates  ^  to  y^  inch  thick,  riveted  together 
and  supported  by  a  mantle  resting  upon  columns.  These  columns 
are  usually  8  or  10  in  number,  and  from  15  feet  to  25  feet  high. 
They  rest  upon  the  main  foundation  of  the  furnace  and  form  a 
circle,  which,  in  large  furnaces,  is  about  30  feet  in  diameter. 
Within  this  circle  the  hearth  is  located.  Its  foundation  must  be 
of  heavy  firebrick  construction.  The  hearth  itself  is  made  of  re- 
fractory firebricks,  and  is  surrounded  and  supported  by  the  hearth 
jacket,  which  is  usually  composed  of  heavy  segmental  iron  or 
steel  castings  or  of  heavy  riveted  steel  plates.  The  cast  jackets 
are  usually  cooled  by  water  flowing  over  troughs,  or  by  coils  of 
wrought  iron  pipe  cast  in  the  jackets.  The  riveted  jackets  are 
cooled  by  external  water  sprays. 

Bosh  Construction. — There  are  two  general  methods  of  con- 
structing the  bosh  walls.  The  choice  between  them  depends  upon 
the  method  of  water  cooling  to  be  adopted.  The  simpler  form  con- 
sists of  a  riveted  plate  jacket,  similar  to  the  shaft  jacket,  which 
is  protected  by  a  thin  lining  of  firebricks,  generally  not  more  than 
9  to  I3J/2  inches  in  thickness.  The  system  of  cooling  consists 
either  of  sprays  of  water  directed  against  the  bosh  jacket  from  all 
sides,  or  of  a  spiral  trough  winding  about  the  boshes  and  kept 
full  of  running  water. 

The  more  usual  method  of  bosh  construction,  however,  is  to 
make  a  thick  bosh  wall  of  fire  bricks,  and  insert  at  intervals  bronze 
cooling  plates.  Cooling  plates  are  hollow  bronze  boxes  tapped  with 
i/4~mch  inlet,  and  i-inch  or  less  outlet  pipes,  so  that  they  may  be 
kept  full  of  running  water.  They  are  usually  wedge-shaped, 
ranging  from*  I  to  3  feet  wide  at  the  nose,  and  as  long  as  the  wall 
is  thick.  They  are  4^  inches  high,  with  a  flat  bottom  and  an 
arched  top  which  tapers  toward  the  nose.  In  order  to  save  bronze 


94  Ftlast  Furnace. 

they  are  sometimes  made  half  length  and  provided  with  a  cast 
iron  box  open  at  each  end,  into  which  they  fit.  These  boxes  sup- 
port the  bosh  wall,  and  facilitate  the  removal  of  the  plates.  Ad- 
jacent plates  are  usually  not  over  4^/2  inches  apart  and  the  vertical 
distance  between  rows  ranges  from  i  to  2  feet.  These  bosh  plates 
are  inserted  at  intervals  from  the  crucible  to  the  mantle.  Above 
the  mantle  two  or  three  rows  of  iron  coolers  are  sometimes  used 
to  protect  the  top  of  the  boshes.  Such  bosh  construction,'  con- 
sisting of  frequent  alternations  of  brickwork  and  cooling  plates 
over  which  the  brick\\  ork  is  carried  by  very  flat  arches,  needs  sup- 
port, and  is  therefore  always  reinforced  by  heavy  bands  of  iron 
encircling  the  furnace  between  the  successive  rows  of  plates. 

Bosh    Plates — Bosh  plates  were  first  used  by  Hunt  in  the 

seventies.  They  consisted  then  of  a  single  coil  of  wrought  iron  pipe 

embedded  in  an  iron  casting.     Cast  iron  melts  readily  and  leaves 

the  iron  pipe  exposed  and  subjected  to  abrasion.     Chving  to  bet- 

rr  A  i  M  E     *er  conducting  qualities  bronze  or  copper  coolers  are  more  erri- 

xxi.,  p.  102.   cjent  ancj  are  now  m  universai  use      Tiie  Fronheiser  plate  was 

introduced  first  at  Cambria.  It  was  a  hollo\v  bronze  box  about 
a  foot  square  and  perhaps  20  inches  long,  tapering  slightly  toward 
the  inner  end.  This  was  set  in  the  brick  work,  and  kept  full  of 
running  wrater.  The  Scott  plate  is  flatter  in  shape.  It  is  i  to  2 
feet  wide  and  only  4^  inches  high,  with  an  arched  top,  and  a 
slight  taper  toward  the  nose.  The  entering  water  Is  led  directly 
to  the  nose  of  the  plate,  and  is  allowed  to  find  its  way  back  through 
a  series  of  baffles  which  divide  the  space  in  the  plate.  The 
Qayley  plate  is  of  similar  shape,  but  has  a  water  space  com- 
prising only  about  10  inches  of  depth  from  the  nose.  The 
Kennedy  plate  differs  from  the  Gayley  in  that  it  has  two  water 
ways  cast  in  metal  instead  of  a  single  large  space.  The  present 
tendency  is  to  use  small  plates  of  the  Scott  type. 

In  wall  Construction. — Above  the  bosh  of  the  furnace  the 
temperature  is  not  so  high  as  to  demand  any  system  for  cool- 
ing. The  causes  for  wear  on  the  lining  of  the  inwalls  are  the 
abrasion  due  to  the  friction  of  the  mpving  particles  of  solid  stock, 
and  the  erosion  of  the  gases.  The  effect  of  moving*  stock  is  min- 
imized, however,  by  the  batter  of  the  \valls.  It  is  most  marked 
at  the  stockline  where  the  charges  strike  the  wall  as  they  slide  off 


Description  of  Plant.  95 

the  distributing  bell.  This  zone  is  often  protected  by  a  shield  of 
steel  plates  or  several  rows  of  cast  iron  plates  set  in  the  brickwork. 
The  erosion  of  the  gases  appears  to  be  more  chemical  than  physical 
in  its  nature.  It  is  usually  greatest  above  the  bosh,  about  two- 
thirds  way  down  the  inwalls. 

Lining. — The  lining  of  the  furnace  is  usually  composed  of  9- 
inch  and  13^ -inch  firebricks.  Except  in  very  large  furnaces,  the 
inwalls  are  usually  27  inches  thick,  and  are  composed  of  fine- 
grained, hard  clay  bricks,  designed  to  resist  abrasion.  The 
"  Woodland  "  brick,  made  by  the  Harbison- Walker  Company  for 
this  purpose  has  the  following  approximate  composition : 

Per  cent. 

Si02 60.65 

Al£Oa 33.81 

Fe2O8 2.14 

CaO 0.41 

MgO    0.33 

The  lining  of  the  boshes,  when  bosh  plates  are  used,  is  also  usually 
27  inches  thick,  but  when  surface-cooled  is  only  9  inches  or  13^2 
inches.  The  lining  of  the  tuyere  zone  is  seldom  less  than  27 
inches  and  the  crucible  walls  are  31^  inches  or  more.  The  hearth 
and  bosh  need  a  more  refractory  brick  than  the  inwalls,  to  endure 
the  higher  temperatures.  A  coarse-grained,  softer  brick  is  gen- 
erally used.  Such  a  brick,  furnished  by  the  Harbison- Walker 
Company  analyses  as  follows : 

Per  cent. 

SiO2 ^._ 53.82 

A1£0S ! 38.12 

Fe203    3.36 

CaO     1.35 

MgO    0.16 

Brick  is  very  soluble  in  furnace  slag,  and  would  not  long 
protect  the  bosh  and  crucible  jackets  from  the  molten  material, 
if  it  were  not  that  early  in  the  operation  of  a  furnace,  a  carbon- 
aceous deposit  replaces  part  of  the  brick  in  crucible  and  bosh 
walls,  and  offers  complete  resistance  to  corrosion.  Such  a  deposit 
develops  best  with  a  hot  and  basic  slag.  Carbonized  bricks  usu- 
ally show  a  composition  within  the  following  limits  : 

Per  cent. 

C    25-50 

CaO     15.30 

..20-45 


/•I last  i' 


If KNACK    OPENINGS. 

Tapping  Hole. — The  furnace  walls  must  be  pierced  for  the 
admission  of  the  blast  and  the  egress  of  products.  The  tapping 
hole  for  the  removal  of  molten  iron  must  be  near  the  level  of  the 
hearth  bottom.  It  is  always  at  the  front  of  the  furnace,  and 
usually  consists  simply  of  a  passage  8  or  10  inches  square  left 
through  the  brickwork.  It  is  stopped  with  clay,  and  owing  to  its 
exposure  to  very  intense  heat  during  the  tapping  of  the  iron  and 
the  danger  of  explosion  when  iron  comes  in  contact  with  leaking 


Composition  of  Cinder  Notch  System. 

water,  attempts  are  seldom   made  to  protect  the  opening  from 
heat.     The  other  openings,  however,  are  always  water-cooled. 

Cinder  Notch. — The  cinder  notch  is  the  opening  designed 
for  the  removal  of  the  accumulated  cinder  or  slag.  There  is  usually 
but  one,  although  the  latest  construction  sometimes  provides  two 
or  three.  Generally,  however,  only  one  is  used  at  a  time.  Its 
location  is  usually  about  90  degrees  from  the  tap-hole.  When 
there  are  two,  they  are  180  degrees  apart.  Since  this  opening  is 
intended  for  the  removal  of  only  that  cinder  which  accumulates 


Description  of  Plant.  97 

between  the  casts  of  iron,  its  location  must  be  above  the  point  to 
which  the  iron  rises,  as  the  time  of  the  casting  is  governed  by  the 
height  of  the  cinder  notch.  Its  height  above  the  hearth  ranges  in 
different  sized  furnaces  from  3^  to  $l/2  feet,  according  to  the 
quantity  of  iron  the  crucible  is  designed  to  hold. 

The  cinder  notch  is  protected,  and  the  flushing  of  cinder  fa- 
cilitated by  a  series  of  water-coolers.  In  the  opening  through  the 
brickwork,  which  is  about  two  feet  in  diameter,  is  first  placed  a 
cooler  which  is  tamped  tight  with  clay.  This  cooler  is  in  shape 
a  hollow  frustrum  of  a  cone,  and  may  be  either  a  coil  of  iron 
pipe,  covered  by  cast  iron,  through  which  water  flows,  or  a  hollow 
bronze  casting  which  can  be  kept  filled  with  water.  The  opening 
through  the  cooler  is  reduced  to  six  inches  by  means  of  a  shorter 
bronze  cooler  called  the  intermediate  cooler.  Within  the  inter- 
mediate cooler  is  a  still  smaller  cooler,  called  sometimes  the 
•* monkey,"  which  reduces  the  opening  to  about  two  inches.  The 
latter  opening  is  closed  by  a  tapering  iron  plug  with  a  long 
handle.  Flushing  is  accomplished  by  simply  withdrawing  the 
plug,  which  is  again  inserted  when  the  cinder  stops  running.  This 
arrangement  is  impossible  in  the  openings  from  which  molten 
iron  flows,  as  the  iron  attacks  the  bronze  and  causes  it  to  leak.  On 
the  other  hand,  a  brick  cinder  notch  would  be  cut  out  rapidly  by 
the  slag,  which,  however,  has  no  effect  upon  the  bronze. 

Tuyeres. — The  openings  for  blast  admission  are  called 
tuyeres.  They  usually  occupy  a  plane  2j/2  to 3  feet  above  the  cinder 
notch,  and  determine  the  maximum  height  to  which  cinder  may 
rise.  The  number  of  tuyeres  in  a  furnace  may  range  from  6  to  24, 
but  12  or  16  are  most  common,  with  recent  preference  for  one  to 
each  foot  of  hearth  diameter.  In  the  tuyere  opening  is  placed  a 
cooler  very  similar  to  the  cinder  notch  cooler.  It  is  usually  of 
bronze,  and  is  set  tight  in  clay.  The  cooler  is  flush  with  the  brick- 
work, both  within  and  without  the  wall  of  the  hearth.  The  tuyere 
is  inserted  in  the  cooler  and  usually  extends  several  inches  beyond 
it.  It  is  of  copper  or  bronze,  hollow  and  water-cooled  like  the 
cooler,  and  not  unlike  it  in  shape,  though  much  smaller.  Its  ex- 
ternal diameter  must  be  such  as  to  fit  snugly  in  the  nose  of  the 
cooler,  to  prevent  leakage.  Tuyeres  present  openings  ranging 
usually  from  4  to  7  inches.  This  opening,  together  with  about  a 


Blast  Furnace. 


2-inch  water  space  all  round  and  bronze  walls  *4  inch  thick  gives 
a  necessary  external  diameter  of  10  to  12  inches.  The  water  space 
in  the  tuyere  and  also  in  the  cooler  is  tapped  for  two  I  ^4-inch 
water  pipes,  through  which  flows  a  constant  and  copious  stream 
of  water.  In  spite  of  this  fact,  the  bronze  is  frequently  "  burned  " 


Cooler. 


Tuyere. 


Blowpipe. 


Composition  of  Tuyere  System. 

through,  and  leakage  of  water  occurs,  thus  necessitating  a  change. 
This  accident  happens  far  more  frequently  to  the  tuyere  than  to 
the  cooler,  since  it  extends  beyond  the  cooler  and  is  consequently 
more  exposed.  The  water  pressure  should  be  about  25  pounds  to 
insure  good  circulation.  Sometimes  the  system  becomes  clogged 
and  hydraulic  or  steam  pressure  should  be  at  hand  to  force  out 


Description  of  Plant.  99 

obstructions  promptly,  or  the  tuyere  will  be  burned  at  the  point 
of  stoppage. 

The  blast  is  transmitted  to  the  tuyere  by  means  of  a  horizontal 
iron  pipe,  known  as  the  blow-  or  belly-pipe.  The  blow-pipes  are 
usually  4  or  5  feet  long,  and  slightly  tapered.  They  are  turned 
with  a  slight  ball  at  the  end  to  correspond  with  a  slight  socket  on 
the  tuyere,  in  order  to  facilitate  the  connection,  as  in  a  universal 
joint.  The  joint  is  purely  a  contact  union,  the  ball  and  socket 
being  used  in  place  of  any  attempt  at  packing. 

Connecting  the  blow-pipe  with  the  distributing  blast  pipe  is  a 
brick-lined  cast  iron  pipe,  known  as  the  leg-pipe,  goose-neck  or 
tuyere-stock.  This  pipe  is  usually  hung  by  lugs  to  eye  bolts  so 
that  it  can  swing  backward,  thereby  releasing  the  blow-pipe  when 
it  is  desirable  to  remove  it.  When  in  place,  the  tuyere-stock  is 
held  firmly  against  the  end  of  the  blow-pipe  by  means  of  a  heavy 
spiral  spring  and  connecting  rod,  reaching  from  a  lug  on  the 
tuyere  stock  to  a  corresponding  anchorage  on  the  hearth  jacket. 
The  longitudinal  pressure  so  developed  furnishes  the  sole  support 
of  the  blow-pipe. 

In  the  back  surface  of  the  tuyere-stock,  in  line  with  the  blow- 
pipe and  tuyere  is  a  i^-inch  hole,  through  which  a  bar  may  be 
thrust  to  clear  the  tuyere,  without  removing  the  blowpipe.  When 
the  blast  is  on,  this  hole  is  closed  by  a  latch,  through  which  is  a 
smaller  opening  closed  by  blue  glass.  This  opening,  which  is 
known  as  the  peep-hole,  enables  one  to  look  through  the  tuyere 
into  the  furnace;  and  thereby  to  get  direct  evidence  as  to  hearth 
conditions. 

The  blast-distributing  pipe,  usually  called  the  bustle-pipe,  en- 
circles the  furnace  at  a  height  about  10  feet  from  the  floor,  and 
connects  with  each  tuyere.  It  consists  of  riveted  steel  plates  and 
has  a  9-inch  lining  of  firebricks.  Its  diameter  varies  with  the 
quantity  of  air  which  it  must  carry,  and  is  usually  4  or  5  feet. 
Into  it  leads  the  hot-blast  main  which  conducts  the  blast  from 
the  stoves. 

TOP   ARRANGEMENTS. 

Besides  the  openings  to  admit  the  blast  and  to  discharge  the 
molten  products  there  is  ordinarily  no  opening  into  the  furnace 


100  Blast  Furnace. 

except  at  the  top,  where  the  materials  enter  and  the  gases  escape. 
The  top  of  the  furnace  was  formerly  left  open,  and  the  escaping 
gases  burned  with  a  constant  flame.  When  it  was  discovered  that 
these  gases  could  be  used  to  heat  the  blast  and  to  generate  power, 
the  bell-and-hopper  device  was  adopted  to  prevent  their  escape. 
A  single  bell  accomplishes  this  object,  except  when  it  is  lowered 
to  dump  a  charge.  Of  late  year? .a  double  bell  system  has  been 
widely  adopted  to  prevent  all  waste  of  gas.  Outlet  for  the  gas 
is  provided  at  one  or  several  points  beneath  the  bell.  These  out- 
lets lead  into  a  large  tube  several  feet  in  diameter,  known  as  the 
"  down  comer  "  or  "  downtake,"  which  conducts  the  gases  to  the 
boilers  and  stoves.  In  some  furnaces  there  are  distributed  about 
the  top  weighted  doors,  known  as  "  explosion  doors,"  which  are 
designed  to  relieve  the  pressure,  caused  by  occasional  explosions 
in  the  top  of  the  furnace. 

Bell  and  Hopper. — The  bell  and  hopper  together  form  an 
annular  V-shaped  depression  into  which  the  stock  may  be  dumped. 
When  the  bell  is  lowered  the  whole  charge  slides  into  the  fur- 
nace. In  order  properly  to  distribute  the  stock,  it  is  found  by 
experience  that  about  two  feet  clearance  all  round  the  bell  gives 
best  results.  The  bell  is  usually  cast  iron,  in  one  or  two  pieces, 
and  of  such  a  slope,  usually  45  degrees,  as  to  admit  of  its  readily 
clearing  itself  of  its  burden.  The  hopper  consists  of  two  pieces, 
the  hopper  and  the  extension-ring.  They  are  also  of  cast  iron 
and  are  usually  made  in  segments.  The  extension-ring  is  sus- 
pended from  a  flange  on  the  bottom  of  the  hopper,  where  it  must 
make  a  gas-tight  joint,  and  yet  be  readily  removed  to  permit  the 
changing  of  bells.  When  in  place  it  serves  to  form  the  joint  be- 
tween the  bell  and  the  hopper.  The  bell  is  usually  suspended  cen- 
trally from  a  counterbalanced  lever,  which  is  controlled  and 
operated  by  means  of  an  air  or  steam  cylinder.  Usually  the  bell 
is  kept  closed  by  this  pressure.  When  the  pressure  is  released 
the  bell  descends  from  the  weight  of  the  charge  upon  it. 

With  the  introduction  of  the  second  bell  it  is  necessary  to  en- 
close the  first  bell  and  hopper  in  a  casing.  The  second  bell  closes 
the  opening  in  the  top  of  the  casing.  Since  both  bells  must  be 
suspended  concentrically  and  yet  be  operated  independently,  it  is 
necessary  that  one  be  hung  on  a  sleeve  surrounding  the  rod  which 


Description  of  Plant.  101 

suspends  the  other.  The  lower  and  larger  bell  is  usually  sus- 
pended on  the  rod  and  the  upper  bell  on  the  sleeve.  Like  the 
single  bell,  they  are  operated  by  horizontal  levers  controlled  by  air 
or  steam  cylinders. 

The  Bleeder — Leading  out  of  the  top  of  the  downtake  is  a 
short  vertical  pipe  of  small  diameter,  called  the  "  bleeder."  It 
allows  surplus  gas  to  escape  from  the  furnace  whenever  necessary. 
It  is  provided  with  a  valve  on  top,  which  may  be  controlled  from 
the  ground. 

Downtake  and  Dustcatcher — The  gases  which  are  generated 
during  iron  smelting  are  highly  combustible,  and  are  used  as  fuel 
to  raise  steam  and  to  heat  the  blast.  At  present,  however,  they 
are  being  largely  applied,  particularly  in  Europe,  to  furnish  power 
by  direct  use  in  gas  engines.  The  gases  are  taken  from  the  fur- 
nace beneath  the  bell  through  outlets,  usually  ranging  in  number 
from  one  to  four,  which  converge  into  a  single  large' pipe  called 
the  downtake.  As  the  current  of  gases  comes  over  into  the 
downtake  with  considerable  velocity,  it  tends  to  carry  along 
fine  particles  from  the  charge.  If  this  dirt  is  allowed  to  go  to 
the  combustion  chambers  of  the  stoves  and  boilers  it  accumu- 
lates there  and  makes  frequent  cleaning  necessary.  Proper 
cleaning  necessitates  the  cooling  of  the  stoves  and  boilers,  which 
causes  not  only  considerable  loss  of  time  and  of  accumulated  heat, 
but  makes  it  necessary  to  have  extra  stoves  and  boilers.  More- 
over, the  alternate  heating  and  cooling  of  the  brickwork  sets  up 
strains,  which  tend  to  disrupt  it.  The  cleaning  is  never  thorough, 
since  fine  particles  adhere  to  the  flue  walls  and,  owing  to  their 
lack  of  conductivity,  reduce  the  efficiency  of  the  heating  surfaces. 

The  purpose  of  the  dustcatcher  is  to  remove  as  much  as  pos- 
sible of  this  dirt.  It  is  virtually  an  enlargement  in  the  down- 
take,  and  depends  for  its  action  upon  the  principle  that  lessening 
the  velocity  of  the  current  will  give  opportunity  for  solid  particles 
to  settle  by  gravity.  It  is  evident  that  the  efficiency  of  a  dust- 
catcher  will  be  in  proportion  to  its  size,  sirice  the  larger  the  cross 
section  of  a  conduit  the  slower  the  rate  of  motion  of  a  given  vol- 
ume of  gases.  This  fact  has  received  more  recognition  in  later 
than  in  former  construction.  The  dustcatchers  of  the  Lacka- 


102  Must  Furnace. 

wanna  Steel  Company's  new  furnaces  at  Buffalo  are  32  feet  in 
diameter.  The  rate  of  motion  of  gases  in  the  downtake  should 
not  exceed  30  feet  per  second.  A  dustcatcher  having  a  diameter 
four  times  greater  than  the  downtake  would  have  a  cross  section 
sixteen  times  greater,  which  would  reduce  the  velocity  of  the 
gases  to  about  2  feet  per  second.  This  velocity  will  not  ordi- 
narily carry  more  than  3^  grains  of  solid  matter  per  cubic  foot. 
Such  gas  may  be  used  in  stoves  and  boilers,  but  is  still  out  of  the 
question  for  gas  engines. 

Gas   Cleaning — In  order  to  get  the  best  results  in  stoves  and 
boilers  the  gases  should  also  be  at  least  partially  washed.     The 


The  Bian  Gas  Washer. 

several  types  of  gas  washers  may  be  classified  under  three  gen- 
eral heads,  as  stationary  scrubbers,  slowly  revolving  washers,  and 
rapidly  revolving  washers  or  centrifugal  machines. 

The  stationary  scrubbers  consist  generally  of  vertical  cham- 
bers  containing  sprays  of  water,  and  sometimes  provided  at  in- 
p.  tervals  with  some  type  of  porous  filter,  which  serves  to  hold  the 
water  in  a  finelv  divided  condition  and  at  the  same  time  to  split 
up  the  current  of  gases  and  bring  the  two  into  intimate  contact. 
The  Zschocke  cleaner  is  a  good  example  of  this  type.  It  brings 

.        ,  , 

i»-16-   the  dust  down  to  about  0.65  grains  per  cubic  foot. 

Revolving  cleaners  consist  essentially  of  stationary  horizontal 
cylinders,  having  through  their  centers  slowly  revolving  shafts, 
carrying  perforated  discs  which  are  half  submerged  in  water. 
The  gases  flow  above  the  water  and  are  forced  through  the  per- 


*  ! 


July  14. 


Description  of  Plant. 


103 


forations  which  are  charged  with  water.  In  this  way  fresh  water 
is  constantly  being  presented  to  the  gases.  The  Bian  apparatus 
is  said  to  wash  40,000  cubic  feet  of  gas  per  minute  with  expendi- 
ture of  about  35  H.  P. 

Such  methods  of  washing  have  their  defects.  They  are  not 
sufficiently  thorough  for  gas  engine  work,  and  they  cool  the  gases 
more  than  is  desirable  for  consumption  in  stoves  and  boilers. 
Less  thorough  methods  answer  all  requirements  for  the  latter 
purpose.  The  Steece  washer,  for  example,  which  gives  satisfaction 


Longitudinal  Section.  Cross  Section. 

The  Theisen  Centrifugal  Gas  Washer. 

at  several  furnaces,  consists  of  a  long  tank  with  a  hopper-shaped 
section  which  is  kept  full  of  water.    The  gases  are  brought  down    iron  Age, 

.  Jan.  22,  1903, 

to  the  surface  of  the  water  repeatedly  by  a  series  of  goose  necks,   p-6- 
and  all  dirt,  except  almost  impalpable  powder,  is  removed  with  a 
loss  in  temperature  of  only  25  degrees  F. 

For  washing  gases  for  use  in  gas  engines  the  centrifugal 
machines  are  so  far  most  successful.  As  they  are  expensive  to 
operate,  they  should  be  used  for  only  that  part  of  the  gas  which 
is  to  be  used  in  the  engines.  Ten  thousand  cubic  feet  per 
minute  is  needed  to  supply  engines  of  5000  to  6000  H.  P.  The 
washing  of  this  quantity  of  gases  in  centrifugal  machines  is  said 


104  Blast  Furnace. 

iron  Age,  to  consume  8ooo  gallons  of  water  and  expend  65  H.  P.  in  24 
'8>  \^'  hours.  The  Theisen  centrifugal  machine  is  largely  used  in 
Europe  for  cleaning  gases  for  engines.  It  consists  of  rapidly 
rotating  cylinders,  in  which  the  gas  enters  at  the  end  and  water 
at  the  periphery.  A  No.  6  washer  is  said  to  clean  30,000  cubic 
feet  of  gas  per  minute  at  expenditure  of  4  H.  P.  per  hour0 
For  use  in  gas  engines  the  gases  should  be  cooled  to  75  degrees  F., 
and  should  not  contain  over  o.i  grain  dust  per  cubic  foot.  In 
this  country  the  first  large  installation  of  blowing  engines 
operated  by  gas,  was  at  the  Lackaw'anna  plant  at  Buffalo.  The 
system  of  washing  in  use  there  consists  of  four  vertical  scrubbers, 
arranged  in  series  and  supplemented  by  centrifugal  machines. 
The  quantity  of  dust  is  easily  reduced  to  o.i  grain  per  cubic  foot. 

Hoisting  Devices. — The  time-honored  method  of  raising  stock 
to  the  top  of  the  furnace  was  to  hoist  it  by  means  of  two  balanced 
cage-hoists,  operated  by  a  single  cable,  controlled  by  the  drum  of 
an  automatic  reversing  hoisting  engine.  The  stock  was  loaded  on 
hand  buggies  at  the  stock  piles  by  the  bottom-fillers,  run  on  the 
scales  and  weighed,  then  run  on  the  hoist  and  sent  to  the  top, 
where  the  top-fillers  dumped  the  buggies  and  returned  them  to  the 
hoist.  With  the  advent  of  larger  furnaces,  making  enormous 
outputs  and  consuming  corresponding  amounts  of  stock,  the  lim- 
itations of  this  system  became  apparent  and  automatic  charging 

was  substituted. 

• 

In  automatic  charging  the  stock  is  usually  sent  to  the  top  in 
self-dumping  skips,  running  up  a  steeply  inclined  skipway.  The 
skips  are  of  much  greater  capacity  than  the  old  hand-buggies,  and 
the  filling  is  consequently  more  rapid.  No  top-fillers  are  needed. 
The  use  of  skips,  however,  demands  special  stock  house  arrange- 
ments. The  ore  and  stone  which  are  stored  in  a  series  of  bins, 
with  discharge  chutes  at  the  bottom,  are  dumped  into  larries  run- 
ning beneath  the  bins,  which  convey  them  to  the  skips.  The  bins 
for  coke  are  usually  arranged  to  discharge  directly  into  the  skip. 
The  larries  are  provided  with  scales,  so  that  the  ore  or  stone  can 
be  weighed  as  drawn  from  the  chutes.  In  this  way  a  larry  with 
two  men  can  handle  as  much  stock  as  twenty  bottom-fillers. 

There  are  several  styles  of  automatic  top  filling  devices.     The 


Description  of  Plant. 


105 


original  arrangement,  the  Neeland  device,  was  installed  at  the 
Dtiquesne  furnaces  of  the  Carnegie  Steel  Company  when  they 
were  built  in  1896.  It  includes  large  cylindrical  buckets,  each  hav- 


The  Julian   Kennedy  Furnace  Top. 


ing  a  small  bell  for  a  bottom.  The  buckets  are  rilled,  run  up  an 
inclined  runway  in  a  carriage,  set  over  the  bell  and  dumped. 
This  method  gives  excellent  results,  but  has  never  been  duplicated. 
In  its  stead  the  self-dumping  skip  has  been  developed.  There  are 


106 


Blast  Furnace. 


Iron  Age, 
May  14,  1903, 
!,.  22. 


Iron  Age, 
Jan.  12,  1905. 


several  types  of  the  skip  hoist  in  use.  They  do  not  differ  much 
in  principle.  The  Brown  system  operates  a  single  large  skip  at 
high  speed.  The  Kennedy  system  operates  two  skips  on  parallel 
tracks.  The  Rust  system  operates  two  skips,  one  passing  over 
the  other. 

The  Julian  Kennedy  furnace  top  has  been  adopted  by  many 
managers.  It  has  been  described  and  well  illustrated  by  Sahlin. 
It  consists  of  a  double  skip-hoist,  the  skipway  being  a  three-girder 
structure,  carrying  double  tracks,  side  by  side.  These  girders  are 
firmly  bolted  to  suitable  foundations,  and  supported  at  the  top 
by  pin-connected  struts  which  bear  on  the  top  of  the  furnace. 
The  skips  are  of  the  self-dumping  variety,  with  the  bale  attached 
at  the  rear,  and  the  rear  wheels  provided  with  wide  treads  to  en- 
gage the  outer  rails  in  dumping.  Hoisting  power  may  be  applied 
either  by  the  usual  vertical  type  of  steam  hoist,  such  as  the  crane 
hoist,  or  by  an  electric  motor-driven  drum.  Either  system  must 
be  of  the  reversing  variety  and  provided  with  automatic  stops 
to  prevent  overhoisting.  The  top  of  the  furnace  is  made  some- 
what conical,  and  is  closed  by  a  cast  steel  lip  ring  and  a  Parry 
bell  of  the  usual  type.  The  whole  is  then  enclosed  in  a  steel  plate 
hood,  ending  at  the  top  in  a  cylinder.  The  bottom  of  this  cylinder 
is  closed  by  the  smaller  bell  and  is  surmounted  by  a  rectangular 
hopper,  into  which  the  skip  dumps.  No  explosion  doors  are  pro- 
vided, as  it  is  claimed  that  they  are  unnecessary,  and  they  only 
serve  to  allow  the  escape  of  stock  during  slips. 

Stock  Distributors. — All  skips  dump  into  receiving  hoppers 
which  drop  the  charge  on  the  upper  bell.  Owing  to  the  fact  that 
in  running  down  an  incline  lumps  tend  to  outstrip  fines,  it  follows 
that  the  side  of  the  hopper  farthest  from  the  skip  will  get  coarser 
material  than  the  near  side.  Furnaces  served  by  skips  often  suf- 
fer from  this  cause  through  the  fact  that  the  gas  tends  to  creep 
up  through  the  more  porous  portions  of  the  charge  and  there 
erode  the  lining.  Every  furnace  so  equipped  very  soon  burns  out 
its  lining  on  one  side,  developing  hot  spots  on  the  shell,  and  thus 
compelling  blowing  out  and  relining.  As  a  result  several  styles 
of  deflectors  have  been  devised  with  a  view  to  distributing  the 
stock  more  evenly. 

The  Brown  distributor  consists  of  a  hopper  in  the  form  of  an 


Description  of  Plant. 


107 


DISTRIBUTOR 
CONE 

Suspended  on 
heels  and 
emovable  tc 

DISTRIBUTOR       X  side  of 
'   rnace 


The  Brown   Stock  Distributor. 


108 


Blast  Furnace. 


Ibid, 

Apr.  12,  1900, 
p.  l. 


Tr.  A.  I.  M    E., 
\\\\   ,  p.  569. 


eccentric  chute,  which  impels  the  charge  to  one  side  of  the  bell, 
but  which  is  geared  so  that  it  rotates  a  given  part  of  the  circle 
each  time  the  skip  comes  up,  thus  causing  the  charge  to  be  dumped 
at  successive  points  in  the  hopper,  as  was  the  case  in  hand  dump- 
ing. This  device  obviates  the  use  of  the  smaller  bell,  as  a  flap 
automatically  closes  the  distributing  chute  whenever  the  bell  is 
lowered. 

The   Baker  &  Neumann  distributing  device  gets  the  effect  of 


The  Baker-Neumann   Stock  Distributer. 


Tr.  A.  I.  M.  E., 
XXX  VII.,  p.  523. 


the  Brown  device  in  a  different  way.  It  is  provided  with  a  de- 
flector plate,  set  at  an  angle  and  attached  to  the  sleeve  hanger 
which  operates  the  small  bell.  The  deflector  is  located  within  the 
simaller  hopper,  just  above  the  small  bell,  and  .when  the  bell  is 
lowered,  compels  all  material  to  fall  on  one  side  of  the  distributing 
bell.  The  sleeve  carrying  the  deflector  is  made  to  rotate  91  de- 
grees each  time  the  bell  closes,  thereby  depositing  the  next  skipful 
in  a  new  place.  This  device  has  proven  its  efficiency. 

Stock  Indicators. — In  hand  charging  a  furnace  it  is  the  duty 


Description  of  Plant.  109 

of  the  top-fillers  also  to  gauge  the  stock  occasionally  to  see  that 
the  furnace  is  kept  full.  This  is  done  by  feeling  with  a  slender 
iron  rod  through  small  holes  left  for  this  purpose  in  the  furnace 
top.  In  the  case  of  automatic  charging,  however,  it  is  necessary 
to  have  some  form  of  automatic  device  to  take  the  place  of  the 
top-filler. 

The  Baker    Stock    Indicator   consists  of  a  steel  rod,  which 
passes  through  the  gauge  hole  to  the  top  of  the  stock,  and  is 
suspended  freely  over  pulleys  by  means  of  a  flexible  connection  p-13- 
which  leads  down  to  the  ground,  and  indicates  the  position  of 
the  rod. 

In  the  Johnson   Automatic    Stock   R  corder    the  flexible 
connection  is  passed  over  a  drum  which  controls  a  dial  on  the   JJjd-14  1905 
stockhouse.    A  recording  pen  makes  a  permanent  record,  which  is  p-i441-' 
a  continual  check  on  the  fillers.    By  means  of  a  rack  and  pinion  the 
rod  is  automatically  lifted  clear  of  the  stock  when  the  bell  is 
lowered. 

HOT    BLAST    STOVES. 

Hot  blast  stoves  are  devices  for  heating  the  blast.  They  are 
usually  located  at  some  point  between  the  blowing  engine  and 
the  furnace  in  order  that  the  blast  may  conveniently  pass  through 
them  on  its  way  to  the  furnace.  They  should  be  placed  as  near 
the  furnace  as  practicable,  as  the  waste  gases  are  always  used 
as  the  fuel  for  heating  them. 

Formerly  all  furnaces  were  blown  with  cold  blast,  and  special 
grades  of  iron  are  still  made  in  that  way.  But  since  the  hot  blast 
was  first  introduced  by  Neilson  in  1828,  its  use  has  been  prac- 
ically  universal.  For  many  years  the  heating  was  accomplished 
by  what  is  known  as  the  "  iron  pipe  stove."  It  consisted  of  a 
series  of  rows  of  cast  iron  U  pipes,  inverted  and  set  in  connecting 
foot  pieces,  forming  continuous  passages  of  great  length,  around 
which  the  gases  were  burned.  The  blast,  passing  through  the 
pipes,  absorbed  the  heat  transmitted  to  it  from  the  burning  gases. 
The  temperature  of  the  blast  from  such  stoves  is  limited  to  about 
900  degrees  F.,  as  the  pipes  deteriorate  rapidly  when  heated 
higher.  There  are  still  many  of  them  in  use  at  old  furnace  plants. 

The  **  firebrick  "  hot  blast  stove  came  into  use  during  the 


HO  Blast  Furnace. 

sixties.  It  has  the  advantage  of  being  able  to  attain  a  temperature 
of  1,500  degrees  F.  It  operates  on  the  Siemens  regenerative  prin- 
ciple, and  hence  is  intermittent  in  its  action.  It  is  first  heated  by 
burning  gas  in  it,  and  then  used  for  heating  the  blast  which  passes 
through  it  in  the  opposite  direction.  There  must  be  at  least  two 
such  stoves  to  each  furnace,  so  that  one  may  be  heating  while  the 
other  is  in  use.  Such  an  arrangement,  however,  would  not  main- 
tain a  very  high  temperature,  since  each  would  be  in  use  half  the 
time.  It  is  necessary,  therefore,  to  have  at  least  three  stoves  to  a 
furnace,  in  order  that  the  period  of  heating  may  be  longer  than 
the  period  of  use.  The  latest  construction  always  allows  for  four, 
in  order  that  the  heating  capacity  may  be  ample  during  cleaning 
and  repairs. 

The  exterior  of  a  stove  consists  of  a  tall,  cylindrical,  riveted 
steel  plate  shell  with  a  dome-shaped  top.  The  stoves  are  usually 
as  high  and  wide  as  the  furnace  itself.  The  extreme  of  size  to 
date  is  that  of  the  stoves  of  the  Lackawanna  Company  at  Buffalo, 
viz.,  135  feet  by  22  feet.  The  shell  is  pierced  for  suitable  inlet 
and  outlet  valves  for  both  gas  and  blast,  as  well  as  air  inlets  and 
blow-off  valves. 

The  interior  of  the  stove  is  of  firebrick  construction,  and  is 
of  many  different  designs.  All  firebrick  stoves  consist  primarily 
of  two  parts,  the  combustion  chamber  and  the  checkenvork.  The 
combustion  chamber  is  an  open  space  reaching  to  the  top  of  the 
stove,  at  the  bottom  of  which  the  gas  is  introduced  and-  burned. 
The  checker  work  consists  of  a  series  of  straight  parallel  firebrick 
flues  leading  from  the  top  to  the  bottom  of  the  stoves.  The  hot 
products  of  combustion  from  the  combustion  chamber  pass 
through  these  flues,  giving  up  their  heat  to  the  walls,  where  it  is 
stored  for  use  in  heating  the  blast.  The  blast  is  heated  by 
passing  it  through  the  stove  in  the  opposite  direction.  It  is  cus- 
tomary to  use  a  stove  for  an  hour  for  heating  the  blast,  then  to 
allow  it  to  absorb  heat  until  its  turn  comes  again.  This  may  be 
for  two  or  three  hours,  according  to  the  number  of  stoves. 

Classification  of  Stoves — Stoves  may  be  classified  according 
to  the  location  of  the  combustion  chamber.  The  side  combustion 
chamber  consists  of  a  segment  of  the  stove  situated  at  one  side 
and  separated  from  the  checkers  by  a  heavy  division  wall,  arched 


PLATFORM    LEVEL 


The  Roberts  Hot  Blast  Stove. 


Ill 


112 


Blast  Furnace. 


toward  the  checkers.  The  central  combustion  chamber,  as  the 
name  implies,  is  situated  concentrically  in  the  centre  of  the  stove. 
The  checkers  are  located  all  around  it. 


HALFi  SECTION  ON   I-J 


HALF  SECTION  ON  G-H 
The  Roberts  Hot  Blast  Stove. 


CHECKER  BRICK 


Stoves  may  also  be  classified  according  to  the  number  of  times 
the  products  of  combustion  pass  through  them.  A  two-pass 
stove  contains  a  combustion  chamber  and  one-pass  of  checkers,  a 


ELEV.    TOP  OF    PLATFORM  -J-  177. 00 


6    VERTICAL   CLEARANCE 


CONE  TO  BE  BUILT  OF  "D>?  BRICK 
AND  "S"  BRICK  PROPORTION  OF 
WHICH  CHANGES  WITU  EVERY  COUR 
TO  SUIT  THE  DECREASING  DIAMS. 


SECTION  THROUGH  GAS  BURNER  AND  HOT  BLAST  VALVE 
The  Julian  Kennedy  Hot  Blast  Stove. 


113 


114 


Blast  Furnace. 


three-pass   stove    has  two  passes  of  checkers,  and  a    four-pass 
stove  has  three  passes  of  checkers. 

The  first  development  of.  the  firebrick  stove  took  place  in 
England,  in  the  form  of  the  Whitwell  type.  The  original  Whit- 
well  stove  had  a  side  combustion  chamber  and  10  small  passes  of 
checkerwork.  When  introduced  into  this  country,  however,  the 
number  of  passes  was  reduced  to  4.  The  type  has  now  become 


The  Julian  Kennedy  Hot  Blast  Stove. 


practically  obsolete.  A  parallel  development  was  the  Cowper 
stove,  which  was  a  two-pass  stove  with  either  side  or  central 
combustion  chamber.  This  type,  under  different  modifications 
came  to  be  used  almost  universally,  first  with  side,  and  later  more 
generally  with  central  combustion  chambers.  There  is  little  to 
choose  between  them.  The  side  chamber  gives  a  greater  checker 
area,  but  the  central  chamber  loses  less  heat  by  radiation  from  the 
combustion  chamber.  There  are  several  surviving  modifications 
of  the  Cowper  type  of  stove,  among  which  may  be  mentioned 


Description  of  Plant. 


115 


those  advocated  by  Roberts,  Kennedy  and  Foote.  The  Roberts 
stoves  are  usually  side  combustion  stoves  of  two  passes ;  the  Ken- 
nedy stoves,  while  having  two  passes,  are  usually  central  com- 


The  Foote  Hot  Blast  Stove. 


bustion  stoves.  The  Foote  stoves  also  are  two-pass,  side-com- 
bustion chamber  stoves,  and  constructed  of  patented  mitre-shaped 
bricks. 

In  all  of  these  stoves,  the  gas  burns  up  through  the  combus- 


116 


Blast  Furnace. 


tion  chamber,  and  the  products  of  combustion  pass  down  through 
the  flues  of  the  checker  work  to  the  chimney  flue.   When  the  stove 


ENLARGED  CROSS  SECTION 
The  Foote  Hot  Blast  Stove. 


CHECKER  BRICK 


is  in  use,  the  blast  is  admitted  by  a  valve  at  the  bottom  of  the 
checkers  and  pursues  the  reverse  course,  passing  out  near  the 
bottom  of  the  combustion  chamber. 

The  three-pass  central  combustion  stove,  used  by  Massick  and 


SECTIONAL  ELEVATION 
The  McClure-Amsler  Hot  Blast  Stove. 


117 


118 


Blast  Furnace. 


p.  864. 


Crookes  and  modified  by  McClure  and  Amsler,  has  a  central  cham- 
ber similar  to  that  of  the  two-pass  stoves.  The  products  of  com- 
bustion are  deflected  by  an  inner  dome  and  made  to  pass  down  an 

Iron  Age, 

May  5. 1892,  annular  set  of  checkers  to  the  bottom  of  the  stove,  only  to  pass 
upward  through  an  outer  annular  set  of  flues  which  discharge  into 
an  individual  chimney  surmounting  each  stove.  The  blast  must, 
of  course,  be  admitted  at  the  top  of  the  stove  and  pursue  the  oppo- 
site course.  It  is  claimed  that  this  arrangement  cools  the  gases 
more  thoroughly  than  the  two-pass  stoves,  and  the  individual, 


SECTION  THROUGH  C-D  SECTION  THROUGH  A-S 

The  McClure-Amsler  Stove. 

symmetrically-placed  chimney  permits  a  more  even  heating  of  the 
flues. 

Stove  Chimneys. — The  hot  blast  stoves  run  usually  in  a 
straight  line  from  the  furnace  toward  the  blowing  engine  house. 
The  draught  chimney  may  be  at  the  end  of  the  row,  but  more  often 
is  midway.  In  some  instances  individual  chimneys  are  used  for 
two-pass  stoves,  because  when  a  single  chimney  is  used,  the  stove 
nearest  it  gets  the  best  draught  to  the  detriment  of  the  others. 
Neither  style  of  chimney  is  entirely  satisfactory  in  the  case  of 
central  combustion  stoves,  as  the  pull  of  the  draught  tends  to  utilize 
the  checkers  nearest  the  chimney  flue  to  the  exclusion  of  the 
others,  and  thereby  reduces  the  working  area  of  the  stove.  This 
objection  is  also  apparent  in  side  combustion  stoves.  It  is  en- 
tirely obviated  in  three-pass  central  combustion  stoves  by  having 
a  central  chimney  on  top  of  the  stove,  thereby  giving  a  symmetri- 
cal draught. 


Description  of  Plant.  119 

Stove  Valves. — The  valve  construction  of  hot  blast  stoves 
presents  a  great  variety  of  forms.  There  are  four  valves  to  be 
considered,  viz.,  the  gas  valve,  the  chimney  valve,  the  cold  blast 
valve,  and  the  hot  blast  valve.  The  cold  blast  valve  is  subjected 
to  the  least  trying  conditions.  Since  it  simply  admits  air  at 
temperatures  somewhat  above  that  of  the  atmosphere,  a  simple 
gate  valve  is  all  that  is  necessary.  The  gas  valve  is  exposed  to 
somewhat  higher,  but  not  excessive  temperatures.  They  should 
never  exceed  that  of  the  furnace  top,  from  500  degrees  to  600 
degrees  F.  This  valve  and  burner  are  usually  the  Spearman  type. 
The  temperature  to  which  the  chimney  valve  is  subjected 
depends  upon  the  degree  to  which  the  checker  work  cools  the 
products  of  combustion.  This  ranges  from  400  to  1000  degrees 
F.  in  different  stoves.  This  valve  is  generally  a  water-cooled, 
mushroom  valve,  although  a  simple  adaptation  of  the  Spearman 
gas  valve  is  meeting  much  favor.  The  hot  blast  valve  is  sub- 
jected to  the  most  trying  condition  of  the  four.  When  the  stove  is 
on  blast,  this  valve  is  constantly  in  the  presence  of  air  at  a  tempera- 
ture far  above  visible  redness,  and  is,  therefore,  the  most  vulnerable 
point  in  the  system.  It  is  generally  of  the  mushroom  type,  water* 
cooled  and  having  a  water-cooled  seat.  A  mushroom  valve  is  usual- 
ly a  hollow  iron  casting,  although  sometimes  it  is  made  of  bronze 
or  other  metallic  composition.  It  has  a  hollow  stem  of  the  same 
metal,  which  is  bolted  to  or  screwed  into  it,  and  by  which  it  is 
raised  or  lowered.  Through  the  stem  passes  a  pipe  for  admitting 
the  cooling  water,  which  finds  egress  through  the  annular  space 
between  the  pipe  and  the  stem.  The  valve  has  a  circular  bearing 
turned  to  fit  the  valve  seat.  This,  being  a  hollow  casting,  is 
also  water  cooled.  The  bearing  of  the  valve  on  the  seat  should 
be  accurately  adjusted,  as  any  leakage  of  the  blast  permits  rapid 
wear  of  the  metal,  especially  if  the  gas  contains  much  dirt.  The 
Berg  hot  blast  seat,  which  is  widely  used,  consists  of  a  hollow 
water-cooled  ring,  clamped  between  two  steel  castings  which  iron  Trade 
face  the  brick  work.  By  loosening  the  clamps  it  may  be  readily  Feb.  1,1900. 
removed  and  replaced. 

The  most  usual  style  of  gas  burner  is  some  modification  of 
the  Spearman  type.  It  consists  of  a  movable  gooseneck,  rising 
out  of  an  underground  gas  flue,  and  leading  horizontally  into 


120 


Blast  Furnace 


The  Kennedy-Morrison  Hot  Blast  Valve. 


Description  of  Plant.  121 

a  gas  port  in  the  side  of  the  stove.  When  not  in  use,  the  goose- 
neck is  racked  back  and  the  port  closed.  When  in  use  the  port 
is  opened,  and  the  gooseneck  racked  forward,  automatically 
opening  the  outlet  of  the  gas  flue.  This  device  is  cumbersome, 
but  it  effectually  prevents  the  leakage  of  gas  into  the  blast  with 
the  attendant  danger  of  explosions.  The  Kennedy-Morrison 
chimney  valve,  which  is  being  widely  applied,  is  of  the  same 
general  form  as  the  Spearman  burner. 

Regulating  Valves. — As  a  rule,  the  hot  blast  main  is  on  the 
same  side  of  the  stove  as  the  gas  main,  and  the  cold  blast  pipe 
on  the  same  side  as  the  stack  flue.  It  is  usual  to  arrange  a  by- 
pass pipe  to  connect  the  cold  blast  and  the  hot  blast  mains. 
This  pipe  is  fitted  with  a  controlling  valve,  by  means  of  which 
cold  blast  may  be  mingled  with  the  hot  blast  to  modify  its  temper- 
ature when  desired.  A  valve  and  escape  pipe,  known  as  the 
"  snort  valve,"  which  can  be  controlled  from  the  cast  house,  is 
always  placed  in  the  cold  blast  main.  It  is  designed  to  permit 
the  throwing  off  of  the  blast  for  any  temporary  cause,  such  as 
closing  the  tapping  hole,  without  stopping  the  engines.  Usually 
a  butterfly  check  valve  is  arranged  to  close  automatically  when 
the  snort  valve  is  open,  in  order  to  prevent  any  gas  backing  up 
to  the  blowing  engines.  This  is  also  the  object  of  a  gas  escape 
valve,  usually  placed  in  the  hot  blast  main  near  the  bustle  pipe, 
which  drops  automatically  when  the  pressure  falls. 

Equalizers. — When  a  fresh  stove  is  put  on  blast,  its  tempera- 
ture may  be  two  or  three  hundred  degrees  above  that  of  the  pre- 
vious stove  when  taken  off.  The  temperature  of  the  new  stove 
will  drop  gradually  during  the  hour  in  use.  At  the  next  change 
there  follows  another  sudden  jump  in  temperature.  Such 
changes  add  to  the  irregular  conditions  under  which  furnaces 
operate.  To  obviate  them,  the  idea  of  an  equalizer  was  evolved 
in  England  in  1901  by  Gjers  and  Harrison.  Their  equalizer  con-- 
sists  of  a  steel  plate  shell,  filled  with  checkerwork,  and  not  unlike 
a  stove  in  appearance.  It  is  55  feet  high  and  20  feet  in  diameter. 
The  checkerwork  is  divided  vertically  in  the  middle  by  an  im- 
pervious wall,  reaching  nearly  to  the  top,  thus  giving  a  two-pass 
arrangement.  The  equalizer  is  placed  between  the  stoves  and 
the  furnace,  and  the  heated  blast  passes  through  it  on  its  way  to 


122 


Blast  Furnace. 


the  furnace.  The  high  temperature  of  the  blast  from  a  fresh 
stove  is  stored  up  to  be  given  out  later  when  the  stove  tempera- 
ture has  dropped.  In  this  way  an  almost  unvarying  blast  tem- 


' 


The  Single  Uehling  and  Steimbart  Pyrometer. 

iron  Age,   perature  is  obtained.     A  small  equalizer,  20  feet  X   12  feet,  has 
I.'   recently  been  installed  at  Stanhope,  N.  J. 

PYROMETRY. 

Pyrometry. — Furnaces  are  usually  provided  with  a  pyrometer 
for  measuring  the  temperature  of  the  blast  and  escaping  gas.  Of 
the  many  varieties  in  existence  the  Uehling  and  Steinbart  is 
most  generally  used  in  this  country.  It  depends  for  its  principle  of 


Description  of  Plant. 


123 


action  upon  the  difference  of  volume  of  air  when  heated  and  when 
subsequently  cooled.     A  chamber  having  an  inlet  opening  and  a 


Diagrammatic  View  of  the  Uehling-Steinbart  Pyrometer 

manometer  tube  dipping  into  water,  connects  with  another  chamber 
having  the  same  sized  inlet  and  a  similar  manometer  tube.  The  lat- 
ter chamber  is  subjected  to  uniform  suction.  The  heated  air  is 


124 


Blast  Furnace. 


iron  Age,  drawn  into  the  first  chamber  by  the  suction  of  the  second,  but  it  is 
l'  cooled  to  212°  F.  before  reaching  the  second  chamber.  The  partial 
vacuum  thus  created  is  indicated  by  the  difference  in  reading  of 
the  manometer  tubes,  which  serves  as  a  measure  of  the  difference 
of  temperature  of  the  blast  before  and  after  cooling  to  212  degrees. 
The  tube  which  receives  the  heated  air  is  usually  tapped  into  the 
hot  blast  main  before  it  reaches  the  bustle  pipe,  but  the  manometers 
may  be  stationed  at  any  convenient  point.  By  means  of  a  pen- 
point  a  continuous  record  of  temperatures  may  be  kept  which 
serves  as  a  check  on  the  hot  blast  conditions. 

Another  type  of  pyrometer  is  the   Le  Chatelier.      It  depends 
for  its  action  upon  the  fact  that  when  a  pure  platinum  wire  is 


Inst.  Jour., 
1904, 


Le  Chatelier  Pyrometer. 

fused  to  one  alloyed  with  10  per  cent,  rhodium  or  iridium,  and 
the  joint  is  heated,  an  electromotive  force  is  set  up  whose  strength 
is  in  proportion  to  the  temperature  which  creates  it.  If  these  two 
P.  loe!  wires  are  connected  to  a  galvanometer  stationed  at  any  suitable 
point,  the  temperatures  may  be  determined  by  means  of  the  gal- 
vanometer deflections.  Such  a  thermo-electric  couple  should  be 
encased  in  a  porcelain  tube  for  protection  before  being  subjected 
to  high  temperatures.  It  has  the  advantage  of  not  being  impaired 
in  efficiency  by  length  of  connections.  The  rhodium  alloy  is  said 
to  be  the  more  durable  of  the  two,  but  the  iridium  gives  greater 
deflection  to  the  galvanometer  needle. 

The  Brown  pyrometer  was  for  a  long  time  used  almost  ex- 
clusively. It  depended  for  its  action  upon  the  expansive  force 
of  heated  metal.  A  thin  strip  of  iron,  placed  in  a  tube,  was  fixed 
firmly  at  one  end  and  attached  to  a  dial  hand  at  the  other.  The  hot 
blast  passing  through  the  tube,  expanded  the  iron  strip,  and  the 
amount  of  expansion  was  indicated  by  the  dial  hand. 


Description  of  Plant. 


125 


THE    CAST    HOUSE. 


The  cast  house  is  the  building  which  shelters  the  pig-bed.  It 
was  formerly  built  of  bricks,  with  arched  doorways,  but  is  now 
generally  of  steel  construction,  and  is  often  provided  with  over- 
head travelling  cranes  for  handling  the  iron  and  for  other  pur- 


Le  Chatelier  Pyrometer  and  Galvanometer. 


poses.  Except  in  the  case  of  furnaces  making  foundry  irons 
exclusively,  the  use  of  ladles  and  pig-casting  machines  for  han- 
dling the  product  has  obviated  the  necessity  for  the  cast  house. 
As  a  result,  it  has  degenerated,  in  the  latest  plants,  into  a  mere 
covering  for  the  runners  and  spouts  which  convey  the  metal  to 
the  various  ladles. 


126  Blast  Furnace. 

THE    BOILER    PLANT. 

The  boiler  plant  of  a  blast  furnace  furnishes  the  power  for 
blowing  the  blast,  for  pumping  the  water,  for  hoisting  the  stock, 
and  also  for  furnishing  the  electricity  for  power  or  lighting.  The 
fuel  is  the  blast  furnace  gases,  sometimes  supplemented  by  coal. 
As  no  gas  can  be  produced  without  power,  it  is  necessary,  when 
blowing  in  a  furnace,  to  start  the  boilers  on  coal.  For  this 
reason  the  boiler  plant  is  always  provided  with  coal  grates  as 
well  as  gas  burners.  Any  standard  type  of  boiler  is  suitable  for  a 
blast  furnace  plant.  The  Babcock  and  Wilcox,  the  Sterling, 
and  the  Cahall  are  perhaps  those  most  universally  used,  although 
many  others  also  give  excellent  satisfaction.  A  furnace  usually 
requires  about  8  boiler  horsepower  for  each  ton  of  coke  burned  in 
24  hours. 

BLOWING   ENGINES. 

Blowing  engines  are  used  to  forced  the  blast  into  the  furnace. 
Until  recently  they  were  usually  driven  by  steam,  but  during  the 
past  few  years  very  important  gas  driven  installations  have  been 
made.  The  turbo-blower  is  also  being  introduced. 

Blowing  engines  are  of  three  general  types :  vertical,  horizontal 
and  vertical-horizontal. 

There  are  three  usual  modifications  of  the  vertical  type.  The 
simplest  form  consists  of  a  simple  engine  having  its  air  cylinder 
directly  above  the  steam  cylinder  with  both  pistons  on  the  same 
rod.  It  is  provided  with  a  fly-wheel  on  each  side,  whose  .crank 
rods  are  connected  with  the  piston  rod  by  means  of  a  long  cross- 
head,  on  account  of  which  it  is  generally  known  as  the  "  long 
crosshead  "  engine.  The  steam  end  may  be  made  either  high  or 
low  pressure,  and  such  a  pair  may  be  operated  as  a  compound 
engine. 

The  most  common  modification  of  the  vertical  type  at  present 
is  the  vertical  cross  compound  connected  engine,  which  consists 
essentially  of  a  pair  of  vertical  engines  provided  with  a  single 
fly-wheel  between  them,  which  obviates  the  use  of  a  long  cross- 
head.  They  have  the  air  cylinders  above  the  steam  cylinders,  as 
in  the  long  crosshead  engine,  and  owing  to  their  great  height  are 
commonly  called  the  "  steeple  "  engines. 


Description  of  Plant. 


127 


The  Vertical  Type  Reynolds  Compound  Engine, 


128 


Blast  Furnace. 


Description  of  Plant. 


129 


130  Blast  Furnace. 

The  third  modification  of  the  vertical  type  is  a  simple  engine 
with  its  steam  and  air  cylinders  on  separate  pedestals.  Conse- 
quently the  respective  pistons  are  operated  by  separate  rods,  which 
connect  with  a  shaft  bearing  a  single  fly-wheel.  The  two  cranks 
are  usually  set  90  degrees  apart  so  that  the  maximum  effort  coin- 
cides with  the  maximum  resistance,  thereby  promoting  smoothness 
of  action.  They  are,  therefore,  generally  known  as  the  "  quarter- 
crank  "  engine.  As  high  and  low  pressure  engines  may  be  oper- 
ated in  pairs,  they  are  more  definitely  described  as  vertical  cross 
compound  disconnected  engines. 

Engines  of  the  horizontal  type  may  also  be  built  single,  com- 
pound connected,  or  compound  disconnected.  They  are  generally 
built  compound  connected,  having  the  steam  and  air  cylinders 
placed  tandem  with  their  pistons  operated  by  a  single  rod  driving 
a  single  flywheel  between,  with  cranks  set  90  degrees  apart,  quite 
similar  to  the  vertical  compound  connected  engine. 

The  vertical-horizontal  type  of  engine  may  also  be  simple  or 
compound.  Usually  the  air  cylinders  are  placed  vertically  and 
the  steam  cylinders  horizontally  in  the  same  vertical  plane.  Since 
the  piston  rods  are  independent  of  each  other  their  cranks  may 
be  set  90  degrees  apart,  and  so  be  classed  also  as  quarter-crank 
engines. 

The  principal  makers  supply  engines  in  all  these  different 
types.  They  are  designed  to  deliver  40,000  to  60,000  cubic 
feet  of  air  per  minute.  They  are  usually  compound  condensing 
engines  having  high  pressure  cylinders,  40  to  48  inches  in  diame- 
ter, and  low  pressure  cylinders  78  to  84  inches  in  diameter.  The 
blowing  cylinders  are  usually  84  to  96  inches  in  diameter,  and  the 
stroke  is  60  or  66  inches.  To  equalize  the  motion  they  have  heavy 
fly-wheels  which  are  designed  to  run  as  high  as  50  revolutions, 
against  a  maximum  pressure  of  30  pounds  per  square  inch,  on 
125  to  150  pounds  steam  pressure.  The  use  of  Corliss  steam 
valves  is  practically  universal.  The  chief  feature  which  distin- 
guishes different  makes  of  engines  is  the  type  of  air  valve. 

The  Koerting  gas  engine  is  used  by  the  Lackawanna  Steel 
Company,  at  Buffalo.  It  is  a  double-acting  two-cycle  engine  of  the 
horizontal-vertical  type,  having  a  horizontal  gas  cylinder  and  a 
Southwark  vertical  air  cylinder,  and  provided  with  a  heavy  fly- 


Description  of  Plant. 


131 


132  Blast  Furnace. 

wheel.  The  length  of  the  gas  cylinder  is  about  double  the  stroke 
of  the  engine,  and  the  length  of  the  piston  is  about  half  that  of  the 
cvlinder.  Each  end  of  the  cylinder  is  provided  with  a  special  slop- 
ing head,  carrying  inlet  valves.  The  exhaust  takes  place  through 
a  series  of  open  ports  midway  in  the  cylinder.  The  length  of  the 
piston  is  so  regulated  that  the  exhaust  ports  are  not  uncovered 
except  at  the  extreme  end  of  the  strokes.  Two  auxiliary  cylin- 
ders, acting  as  simple  piston  valves,  are  arranged  to  pump  the  gas 
and  air  respectively  to  both  ends  of  the  working  cylinder  in  quan- 
tities suitable  for  mixture.  They  are  driven  by  a  crank  no  de- 
grees in  advance  of  the  main  crank.  The  inlet  valve  is  opened 
before  the  main  crank  reaches  the  dead  center.  The  air  enters 
first  and  part  of  it  goes  to  sweep  out  the  exhaust  gases  and  form 
a  cushion  between  them  and  the  fresh  gas.  The  new  mixture  is 
compressed  to  10  atmospheres  by  the  returning  piston  and  at 
dead  center  two  electric  igniters  start  combustion.  The  engines 
are  rated  at  2000  horsepower  each,  and  deliver  about  20,000  cubic 
feet  of  air  up  to  30  pounds  pressure  per  minute  of  60  revolutions. 


CHAPTER  III. 
OPERATION  OF  THE  FURNACE. 

Introductory.  —In  no  business  are  good  judgment  and  long 
experience  more  important  than  in  the  operation  of  a  blast  fur- 
nace. They  are  necessary,  not  only  to  the  manager,  but  to  each 
employee.  The  organization  of  a  blast  furnace  force  must  be 
such  that  each  person  has  his  specific  duties,  for  which  he  alone  is 
responsible.  Each  turn  is  in  the  care  of  a  general  foreman  or 
founder,  sometimes  called  the  "  blower,"  who  maintains  a  general 
supervision  over  the  furnace  and  all  of  its  accessories.  The  fur- 
nace itself  is  in  charge  of  a  •'  keeper,"  who  supervises  tfye  tapping 
of  iron  and  cinder,  and  also  watches  the  condition  of  the  furnace 
both  within  and  without.  He  is  usually  provided  with  two  or 
more  "  helpers, "who  assist  about  the  furnace.  The  skimmer  and 
runners  are  the  especial  care  of  the  first  helper,  the  pig  bed  and 
the  running  of  the  iron  of  the  others.  The  care  and  disposal  of 
the  cinder  and  slag  are  in  charge  of  slag  men,  or  "cinder  snap- 
pers," as  they  are  generally  called.  A  stove  tender  looks  after 
the  hot  blast  stoves,  and  the  stock  is  handled  by  the  fillers. 

BLOWING   IN. 

Drying   the    Furnace — When  a  newly-built  furnace,  or  an 

old  one  which  has  been  freshly  lined  with  bricks,  is  about  to  be 
put  into  blast,  it  should  first  be  subjected  to  careful  drying  to  re- 
move all  moisture  from  the  new  brickwork.  This  is  usually  accom- 
plished by  means  of  a  wood  fire  built  in  the  hearth.  The  drying 
should  be  gradual  to  prevent  any  undue  shrinkage  or  cracking  of 
the  brickwork.  It  is  begun  by  means  of  a  light  fire,  which  is 
gradually  increased  to  sufficient  intensity  to  insure,  completeness. 
Formerly  it  was  thought  necessary  to  consume  two  weeks  in  the 
operation,  but  now  many  managers  consider  one  week  sufficient. 
Filling  the  Furnace  — The  operation  of  smelting  iron  is  in- 
augurated by  filling  the  furnace  with  cold  stock  and  subsequently 
.lighting  it.  As  failure  in  properly  lighting  a  furnace  may  entail 


134  Blast  Furnace. 

great  expense,  the  filling  should  be  done  carefully.  The  general 
method  consists  of  first  placing  wood  on  the  hearth,  and 
following  it  with  a  large  body  of  coke,  upon  which  is  built 
a  succession  of  light  but  gradually  increasing  charges  of 
ore,  properly  fluxed.  The  first  layer  of  wood  is  sometimes 
deposited  directly  on  the  hearth,  but  usually  on  a  scaffold 
about  the  level  of  the  tuyeres.  It  consists  of  cordwood  sticks 
placed  on  end.  Sometimes  as  many  as  three  such  layers 
of  wood  are  used,  thus  bringing  the  top  of  the  wood  well  up  into 
the  boshes.  Upon  the  wood  is  placed  a  blank  charge  of  coke, 
mingled  with  a  sufficient  quantity  of  limestone  to  flux  its  ash,  and 
10  to  25  per  cent,  of  gray  blast  furnace  cinder  to  prevent  too  high 
alumina  in  the  slag.  This  blank  charge  of  coke  varies  usually 
from  one-third  to  one-half  the  cubical  contents  of  the  furnace. 
It  is  advisable  to  charge  plenty  of  coke  at  this  point  so  that  the 
furnace  may  be  hot  and  gray  from  the  start.  Upon  this  bed  of 
coke,  the  charges  of  fuel,  ore  and  flux  are  begun.  The  first  five 
to  ten  rounds  of  fuel  are  accompanied  by  light  charges  of  ore, 
usually  about  half  the  weight  of  the  fuel.  Sufficient  limestone  to 
flux  the  gangue  of  the  ore  and  the  ash  of  the  fuel  is  added,  to- 
gether with  an  equal  quantity  of  blast  furnace  cinder.  With  each 
subsequent  series  of  five  to  ten  rounds  of  fuel,  the  ore  and  stone 
are  increased,  and  the  cinder  diminished,  until  by  the  time  the 
furnace  is  full,  the  ratio  of  fuel  to  ore  is  about  i  :  I.  After  blow- 
ing in,  the  ratio  is  gradually  increased  from  day  to  day,  as. fast  as 
is  warranted  by  the  temperature  of  the  hearth,  as  shown  by  the 
quality  of  cinder  and  iron  produced.  Usually  the  normal  burden 
is  reached  within  a  week  or  ten  days. 

Lighting  the  Furnace.  -When  the  furnace  has  been  com- 
pletely filled  it  is  ready  to  light.  The  space  beneath  the  scaffold  is 
filled  with  kindling,  and  a  quantity  of  kerosene  oil  is-  poured  into 
each  tuyere.  The  bell  is  closed  and  the  bleeder  opened,  and  all 
the  gas  burners  at  both  boilers  and  stoves  are  closed  tight.  Light 
blast  is  then  turned  on,  and  fire  is  started  .simultaneously  at  all 
the  tuyeres  by  means  of  a  red-hot  iron  rod  thrust  through  the 
pricker  hole.  In  two  or  three  minues,  smoky  gas  appears  at  the 
top  of  the  furnace.  This  should  be  ignited  at  once.  The  bell  is  kept 
closed  and  the  bleeder  kept  open  until  all  of  the  wood  smoke  disap-. 


Operation  of  the  Furnace.  135 

pears  and  the  gases  burn  clearly  and  freely  at  the  top.  Then  the 
bell  is  closed  and  the  gases  find  their  way  into  the  downtake.  The 
gas  burner  farthest  from  the  furnace  on  the  boiler  line  may  then 
be  cautiously  opened  till  the  gas  ignites.  As  the  volume  of  gas  in- 
creases, other  burners  may  be  turned  on.  These  precautions  are 
imperative  in  order  to  avoid  the  disastrous  explosions  which  fre- 
quently result  from 'igniting  gas  before  all  the  air  has  been  swept 
out  of  the  pipes.  The  gases  are  especially  dangerous  during 
blowing-in.  Explosions  are  extremely  liable  to  happen  and  the 
effects  of  inhalation  are  rapid,  violent  and  sometimes  fatal.  These 
phenomena  are  due  to  the  abnormally  high  percentage  of  CO  in 
the  gases  while  the  coke  blank  is  burning  and  reduction  is  not 
rapid.  Analyses  of  gases  which  are  given  off  by  the  furnace 
during  blowing-in  show  that  when  the  furnace  is  first  lighted, 
combustion  is  nearly  complete,  and  little  CO  is  formed.  After  an 
hour  or  so,  the  mass  of  coke  becomes  heated  to  the  temperature 
where  it  can  react  upon  CO2,  reducing  it  to  CO.  The  ratio  of  CO  xxvni.?1' E' 
to  CO2  may  then  rise  to  10,  making  the  gas  very  dangerous.  The  p-608- 
ratio  soon  falls  to  about  5,  whence  it  is  gradually  reduced  as  the 
burden  rises  to  normal. 

Danger  in  Carbonic  Oxide. — The  effect  of  CO  on  the  human 
system  is  highly  poisonous.  Even  when  very  much  diluted  by 
air  it  is  dangerous,  and  its  effects  are  cumulative.  It  is  said  that 
exposure  for  an  hour  t'o  air  containing  small  quantities  of  it 
produces  the  following  result : 

0.20  per  cent,  produces  giddiness. 

0.35  per  cent,  produces  inability  to  walk.  JjJJ*-  J oltr 

0.70  per  cent,  produces  unconsciousness.  p.  395 

1.00  per  cent,  is  very  dangerous. 

When  in  its  natural  state,  blast  furnace  gas  is  both  visible 
and  odorous.  When  cooled  and  washed  it  is  neither,  and  hence  is 
very  insidious,  particularly  when  used  in  gas  engines.  It  per- 
meates soil  and  masonry,  especially  when  heated.  Hence  they 
should  be  rendered  impervious  by  cement  or  concrete.  Leaks 
may  be  detected  by  introducing  in  the  mains  a  strongly  odorous 
substance,  such  as  acetylene.  Mice  and  birds  are  quickly  affected 
and  so  may  serve  as  tests  for  doubtful  places. 

Tapping  the  Furnace — Within  10  to  15  hours  after  the  blast 


136  Blast  Furnace. 

is  put  on,  the  slag  will  have  accumulated  in  sufficient  quantity  to 
reach  the  level  of  the  cinder  notch.  By  watching  through  the 
peep  hole,  the  keeper  can  see  when  the  slag  rises  to  the  level  of 
the  tuyeres.  The  cinder  is  then  flushed.  Three  or  four  flushes 
usually  take  place  before  much  iron  accumulates  in  the  hearth. 
Usually  20  to  30  hours  after  the  lighting  of  the  furnace,  the  iron 
is  ready  to  tap.  The  tap  hole  is  generally  opened  by  means  of  a 
hand  drill,  but  it  is  being  replaced  in  some  localities  by  a  motor 
drill  operated  by  compressed  air.  When  the  drill  has  cut  away 
the  clay  until  it  shows  bright  red,  a  bar  is  driven  into  the  hole 
with  sledges.  The  opening  so  made  is  quickly  enlarged  by  flowing 
metal,  which  is  then  directed  by  the  helpers  into  its  proper 
channels. 

METHODS    OF  HANDLING   PRODUCTS. 

There  are  two  general  methods  of  handling  the  iron  which 
flo\vs  from  the  furnace,  viz. :  cold,  in  pig-beds,  and  molten,  in 
ladles. 

CASTING   IN   PIG-BEDS. 

Sand  Pig-Beds. — Formerly  all  the  iron  was  handled  in  sand 
pig-beds.  By  means  of  wooden  patterns  a  series  of  parallel,  ad- 
jacent depressions,  about  40  inches  long,  4  inches  wide  and  4 
inches  deep,  are  moulded  in  loose,  moist  sand.  These  depressions 
are  connected  to  the  main  runner,  which  leads  from  the  tap-hole 
by  means  of  a  cross  runner  which  connects  with  one  end  of  each 
depression.  Into  these  depressions  the  molten  iron  is  led.  Owing 
to  a  fancied  similarity  in  appearance,  the  iron  in  the  cross  runner 
is  known  as  the  "  sow,"  and  that  in  the  parallel  depressions  as 
the  "  pigs."  As  soon  as  the  iron  is  fairly  set,  it  is  covered  with  a 
layer  of  sand  which  is  scattered  over  it  by  the  shovelful.  Then, 
by  means  of  bars  and  sledges  the  pigs  are  broken  from  the  sow, 
and  the  sow  broken  into  convenient  lengths.  The  purpose  of  the 
sand  covering  is  twofold :  to  protect  the  workmen  from  the  in- 
tense heat  of  the  iron,  and  to  retard  the  cooling,  thereby  facilitating 
breaking  the  iron  and  incidentally  increasing  the  size  of  the  grain. 
The  pigs  are  then  cooled  by  a  spray  of  water,  loaded  on  trucks  by 
hand  and  taken  to  the  wharf  where  they  are  broken  and  piled, 
ready  for  shipment.  This  method  of  handling  the  iron  permits 


Operation  of  the  Furnace.  137 

cooling  in  a  bed  of  slowly-conducting  material,  thereby  allowing 
large  crystals  to  develop  in  the  pig.  On  the  other  hand,  it  per- 
mits the  adhesion  of  much  sand,  which  is  undesirable  in  iron 
intended  for  basic  steel  manufacture.  The  sand  pig-bed  is  de- 
stroyed by  use,  and  must  be  remade  before  each  cast. 

Chills — A  modification  of  the  sand  pig-bed  is  the  iron  pig- 
bed,  known  as  "  chills."  It  comprises  a  permanent  pig-bed,  which 
is  composed  of  heavy  iron  castings  moulded  in  shape  very  similar 
to  that  of  the  sand  pig-bed.  Such  a  bed  requires  no  preparation 
beyond  sweeping  and  sprinkling  with  clay  wash  before  each  cast. 
The  heat  of  the  chill  dries  the  wash,  leaving  a  coating  of  clay, 
which  prevents  sticking  and  cutting  or  melting  of  the  chills.  The 
iron  is  run  into  it,  cooled  and  broken  in  the  same  way  as  in  the 
sand  bed.  The  resulting  iron  is  free  from  adhering  sand;  hence 
this  system  is  advantageous  in  making  iron  for  steel  manufacture. 

Pig  Breakers. — Sometimes  pigs  are  handled  by  overhead 
cranes,  which  transport  the  unbroken  sections  of  the  cast  to  a  pig- 
breaker.  Such  a  device  was  installed  at  the  Duquesne  plant,  and  is 
still  occasionally  used.  The  pig-bed,  instead  of  being  in  the  usual 
form,  consisted  of  long,  parallel  pigs  or  sows,  about  20  feet  long, 
joined  together  in  pairs.  This  was  a  convenient  shape  for  the 
breaker.  The  breaker  consists  of  a  heavy  plunger,  working  over 
a  table  by  means  of  an  eccentric  shaft.  The  breaker  is  fed  by  a 
bed  of  motor-driven  live  rolls,  that  bring  the  piece  to  be  broken 
under  the  oscillating  plunger.  The  broken  pigs  slide  from  the 
breaker  into  cars. 

At  the  plant  of  the  Buffalo  Susquehanna  Company  the  iron  is 
run  in  sand  beds  and  when  cooled  sufficiently  is  picked  up  by  a 
travelling  crane  and  taken  to  a  Brown  Pig  Breaker,  where  it  is 
broken  for  shipment. 

CASTING    IN    LADLES. 

As  furnaces  increased  in  size  and  capacity,  they  produced  such 
enormous  quantities  of  iron  at  each  cast,  that  the  pig-bed  system 
became  impracticable.  Moreover  it  was  found  to  be  cheaper  in 
the  case  of  steel  manufacture,  to  take  the  iron  directly  to  the  steel 
furnaces  in  the  molten  condition.  For  these  reasons,  the  system 
of  handling  it  in  ladles  was  adopted.  This  method  has  come  into 


138 


Blast  Furnace. 


such  general  use  that  at  present  a  large  percentage  of  all  pig 
intended  for  steel  making  and  also  some  "foundry  pig  is  tapped 
into  ladles,  and  a  decreasing  percentage  of  the  total  output  of 
the  country  is  run  into  pig-beds. 

For  the  use  of  the  ladle  system  of  handling  iron,  it  is  necessary 
that  the  iron  runner  should  branch  to  a  series  of  spouts  at  least 
equal  in  number  to  the  ladles  needed  to  hold  a  cast.  These  spouts 
should  be  at  such  an  elevation  that  the  ladles  may  be  stationed  on 


The  Berg  Hot  Metal  Ladle. 

tracks  beneath.  Each  ladle  should  hold  20  tons  or  more  and  still 
have  margin  to  allow  for  slopping.  When  the  ladles  are  filled  the 
iron  is  covered  with  coke  dust  and  sent  to  the  steel  mill. 

Hot  Metal  Ladles.  —  There  are  many  makes  of  hot  metal 
ladles,  which  differ  only  in  minor  details.  Those  manufactured  by 
the  Pollock  Company,  of  Youngstown,  Ohio,  from  the  Berg  pat- 
i  W.  ents,  will  serve  as  a  type.  The  ladle  bowl  is  made  of  heavy,  riveted 
plates,  set  in  a  steel  cast  trunnion-ring,  and  lined  with  fire  bricks. 
The  running  gear  consists  of  two  single  trucks  connected  by  a 
steel  cast  frame  to  which  a  steel  cast  buffer  is  strongly  riveted. 


° 


Operation  of  the  Furnace. 


139 


Couplers,  journal-boxes,  etc.,  are  of  the  usual  M.  C.  B.  patterns. 
The  trunnions  are  in  the  form  of  pinions  and  work  in  racks,  so 
that  as  the  ladle  tilts,  it  travels  forward.  The  tilting  is  accom- 
plished by  means  of  a  worm  gear,  which  may  be  operated  by  hand 
or  by  power. 

The  Treadwell  hot  metal  ladle  is  constructed  on  similar  lines. 

PIG  CASTING   MACHINES. 

If  the  steel  mill  were  in  a  position  to  receive  the  product  of 
the  blast  furnace  continuously,  a  series  of  ladles  would  be  the  only 


10,1903. 


The  Berg  Cinder  Ladle. 

handling  equipment  necessary.  But  in  order  to  handle  the  output 
of  iron  when  the  mill  is  shut  down  or  over  Sundays,  or  in  the  case 
of  iron  that  must  be  allowed  to  cool  for  shipment,  a  further  device 
is  needed.  For  this  reason,  mechanical  pig-beds,  known  as  pig 
casting  machines,  have  been  devised.  They  were  first  used  by 
furnaces  operated  in  conjunction  with  steel  plants,  but  were  later 
adopted  by  isolated  furnaces,  even  those  making  foundry  pig. 


140  Blast  Furnace. 

A  pig  casting  machine  consists  essentially  of  a  series  of  moulds, 
which  are  made  to  pass  successively  under  a  spout  into  which  the 
molten  iron  in  the  ladle  is  poured.  There  are  several  kinds  of 
pig  casting  machines,  which  may  be  classed  under  two  types,  the 
endless  chain  and  the  circular  disc. 

Endless  Chain  Machines — The  leading  examples  of  the 
endless  chain  type  are  the  Heyl  and  Patterson  and  the  Uehling 
machines. 

The  Heyl  and  Patterson  machine  consists  essentially  of  a 
pair  of  endless  chains,  supported  by  wheels  which  run  on  a  track, 
and  which  carry  a  series  of  pressed  steel  moulds.  The  trackway  is 


The  Heyl  and  Patterson  Pig  Casting  Machine. 

approximately  horizontal,  except  at  the  delivering  end,  where  it 
May  is,  i89»!  rises  so  that  the  pigs  may  fall  into  railway  cars  as  the  moulds 
reverse  themselves.  A  portion  of  the  horizontal  track  is  de- 
pressed and  passes  through  a  tank  full  of  running  water,  which 
cools  the  pigs  enough  for  handling.  After  the  moulds  dump  their 
burden  at  the  delivering  end,  they  return  to  the  receiving  end 
on  a  lower  trackway  in  an  inverted  position,  passing  over  smoke 
ovens  or  tar  swabs,  which  give  them  a  carbonaceous  coating  to 
prevent  the  iron  from  sticking.  The  endless  chain  is  driven  by  a 
pinion  shaft,  each  pinion  being  equipped  with  a  friction  clutch. 
A  pair  of  chains  will  handle  1500  tons  in  24  hours  with  expendi- 
ture of  14  horsepower  per  hour. 

The  Uehling  Pig  Casting  machine  was  the  first  which  proved 
successful.  It  consisted  of  a  series  of  moulds  on  an  endless  chain 
which  dumped  into  a  tank  of  water  at  the  turn.  The  present  form 


Operation  of  the  Furnace.  141 

is  divided  into  two  sections,  the  first  being  the  casting  machine, 
and  the  second  the  cooling  conveyor.  Each  section  consists  of  an 
independent  endless  chain.  On  the  casting  section  the  moulds  are 
of  cast  iron  and  no  cooling  water  is  used.  By  the  time  the  pigs 
reach  the  end  of  the  casting  section,  they  are  sufficiently  solidified 
to  be  discharged  to  the  cooling  conveyor.  On  the  return  strand 
the  moulds  pass  over  a  lime  vat  in  the  inverted  position  and  re- 
ceive a  spray  of  milk  of  lime,  which  forms  a  protective  coating. 
The  cooling  conveyor  is  of  similar  construction,  except  that  the 
moulds  are  replaced  by  steel  plates  which  receive  the  pigs,  carry 
them  through  a  large  trough  filled  with  water  and  dump  them  on 
cars.  This  section  may  be  set  in  line  with  the  casting  section,  or, 
if  economy  of  space  is  desirable,  at  right  angles  to  it. 

Both  of  these  machines  are  now  made  by  the  Heyl  and  Patter- 
son company.  The  essential  differences  between  them  are  as 
follows :  The  Heyl  and  Patterson  machines  use  pressed  steel  pans 
with  a  tar  coating,  and  the  pig  is  plunged  in  water  very  early. 
The  Uehling  machine  uses  cast-iron  pans,  coated  with  lime,  and 
the  cooling  by  water  is  later.  The  first  cost  of  the  Heyl  and  Pat- 
terson machine  is  less  than  that  of  the  Uehling,  but  the  operating- 
expenses  and  the  losses  of  metal  are  said  to  be  greater.  The  cost 
of  maintaining  and  operating  the  machines  usually  ranges  from 
15  to  22  cents  per  ton  of  pig  made.  This  is  about  equally  divided 
between  operating  and  maintenance. 

Disc  Machines. — The  disc  machines  have  not  met  with  as 
much  favor  as  the  endless  chain  machines.  The  leading  example  is 
the  Davies  machine.  It  consists  of  a  horizontal  revolving  wheel, 
about  40  feet  in  diameter,  with  a  series  of  moulds  on  its  periphery. 
The  moulds  are  rectangular  cast  iron  blocks,  having  depressions  on 
all  four  sides,  which  serve  as  moulds  in  turn  and  thereby  prolong 
the  service  of  each  mould.  The  moulds  pass  under  the  pouring 
spout,  and  the  pigs  become  solidified  by  the  time  half  the  circle  is 
traversed,  when  they  are  dumped  into  a  tank  of  water.  The 
moulds  are  then  sprayed  with  milk  of  lime,  and  are  ready  for  a 
fresh  charge  by  the  time  they  reach  the  spout. 

SAMPLE   FOR   ANALYSIS. 

It  is  customary  to  take  one  or  more  samples  of  the  iron  while  it 
flows  from  the  furnace  for  purposes  of  analysis.  Proper  sam- 


142  Blast  Furnace. 

pling  is  very  important,  in  order  that  analysis  may  represent  a 
fair  average.  The  duty  of  sampling  usually  devolves  upon  the 
stove-tender.  It  is  accomplished  by  means  of  a  wrought  iron  or 
soft  steel  spoon,  6  or  8  inches  in  diameter,  with  a  4-foot  handle. 
The  spoon  is  first  washed  with  clay  suspended  in  water,  to  protect 
the  bowl,  and  to  prevent  the  metal  from  sticking  to  it.  It  is  then 
dipped  cautiously  into  the  flowing  metal,  and  its  contents  poured 
into  a  small  mould,  making  an  ingot  about  5x2x1  inch,  or 
poured  into  a  pail  of  water  which  granulates  the  metal  in  the  form 
Am.  soc.  Test  of  shot.  Shot  samples  are  generally  slightly  lower  in  Si  and  notably 
v.,  p.  zi6,  lower  in  S  than  ingot  samples.  If  only  one  sample  is  taken  it  is 
imperative  to  wait  until  the  iron  has  flowed  some  minutes,  in  order 
to  insure  a  fair  average,  as  the  composition  at  the  beginning  of 
the  flow  may  differ  considerably  from  that  at  the  end.  If  several 
samples  are  taken,  they  are  distributed  through  the  flow.  One 
should  be  taken  every  5  to  10  tons  of  metal.  The  advisability  of 
these  precautions  becomes  apparent  from  the  following  analyses : 

Si.  S. 

1st  bed 1.99  0.024 

3d  bed 2.17  0.022 

5th  bed 2.29  0.024 

7th  bed J 2.46  0.024 

,„  ^jj             9th  bed 2.57  0.027 

llth  bed ! 2.GO  0.023 

13th  bed 2.60  0.022 

15th  bed 2.85  0.020 

17th  bed 2.36  0.019 

19th  bed 1.80  0.023 

SKIMMING    THE    IRON. 

Since  the  tapping  hole  is  approximately  level  with  the  bottom 
of  the  crucible,  it  follows  naturally  that  what  flows  from  the  fur- 
nace first  is  iron  practically  free  from  slag.  Later,  and  especially 
toward  the  end  of  the  cast,  the  slag  comes  freely.  Since  it  is 
about  one-third  of  the  specific  gravity  of  the  iron,  it  floats  upon  it, 
and  can  be  easily  separated  by  '*  skimming."  Skimming  devices 
all  include  a  depression  in  the  iron  runner,  followed  by  a  dam,  over 
which  the  iron  must  rise  before  it  can  flow  to  its  receptacles.  The 
skimmer  is  suspended  across  the  runner  over  the  depression  at 
such  a  height  that  it  rests  on  the  top  of  the  stream  of  iron  and 
effectually  prevents  the  slag  from  being  carried  over  the  dam. 


Operation  of  the  Furnace. 


143 


The  slag  is  allowed  to  overflow  at  the  side,  and  is  conducted  to 
suitable  receptacles. 

Formerly  it  was  customary  to  mould  a  dam  in  a  sand  runner 
before  each  cast,  and  an  iron  plate  skimmer  was  suspended  across 
the  trough  and  was  raised  or  lowered  during  the  cast  as  occasion 
demanded.  The  iron  left  in  the  trough  after  casting  was  drained 
off  by  tearing  down  the  dam  with  a  hook.  This  iron,  mixed  with 


General  View. 


Section  of  Skimmer. 
The  Killeen  Skimmer  and  Metal  Trough. 


sand,  flowed  into  the  beds  or  ladles.  The  making  of  a  dam  was 
always  a  delicate  task,  and  a  test  of  a  furnaceman's  skill.  A  bad 
dam  might  result  in  considerable  loss,  by  allowing  the  iron  and 
slag  to  mix,  unless  the  skimmer  was  manipulated  quickly.  The 
constant  watching  of  a  skimmer  is  not  a  pleasant  occupation,  par- 
ticularly when  lead  or  arsenical  ores  are  used.  While  furnaces 
remained  small  and  comparatively  small  quantities  of  iron  were 
tapped  every  six  hours,  this  method  was  adequate.  With  rapidly 


144  Blast  Furnace. 

growing    furnaces    and    outputs    came    changes    in    skimming 
devices. 

Killeen  Skimmer. — The  Killeen  skimmer  was  adopted  by  the 
Carnegie  Company,  and  the  use  of  its  various  modifications  is 
fast  becoming  universal.  It  consists  of  a  permanent  cast  iron 
trough,  made  in  the  shape  of  the  old  sand  runner  and  dam.  Just 
in  front  of  the  dam  are  slots  cast  in  the  side  of  the  trough  to 
receive  the  skimmer.  A  depression  in  one  side  of  the  trough  in 
NOV.  i«,  i8»o',  front  of  the  skimmer  allows  for  the  overflow  of  the  skimmed  slag. 
An  outlet  in  the  side  of  the  trough,  between  the  skimmer  and  the 
dam.  is  provided  for  draining  the  iron  after  the  cast.  To  prepare 
such  a  dam  no  skill  is  needed  beyond  the  ability  to  smear  it  with 
clay  to  prevent  corrosion.  The  trough  is  deep  and  wide,  and  is 
amply  able  to  care  for  sudden  rushes  of  iron  or  slag.  After  the 
iron  has  ceased  to  flow  from  the  furnace,  the  drain  gate  is  raised 
slightly  to  allow  the  iron  in  the  trough  in  front  of  the  dam  to  drain 
into  the  ladles. 

CINDER  OR   SLAG. 

Blast  furnace  cinder  and  slag  are  identical  in  nature.  They 
comprise  the  molten,  non-metallic  products  of  the  operation.  In 
practice,  however,  there  is  a  distinction  made  between  them  which 
has  no  foundation  in  difference.  What  is  generally  known  as 
"  cinder  "  is  flushed  from  the  cinder-notch  between  casts.  The 
cinder  which  accompanies  the  iron  at  casting  time,  however,  is 
distinguished  by  the  term  ••  slag."  Properly  speaking,  it  is  all 
slag,  since  slag  is  the  scoria  from  any  smelting  operation.  The 
term  "  cinder  "  probably  resulted  from  the  fact  that  it  includes  the 
ashes  and  cinders  of  the  fuel  which  must  be  removed  by- fluxing, 
since  they  cannot  be  raked  out  as  in  the  case  of  ordinary  fires. 

Disposal  of  Slag. — Three  general  methods  for  the  disposal  of 
slag  may  be  distinguished ;  in  gutters,  in  ladles,  and  in  granulation 
pits. 

Allowing  the  cinder  to  cool  in  depressions  in  the  earth  is  an 
old  and  crude  method  of  disposal.  It  is  expensive,  as  it  entails 
much  labor  in  subsequent  loading  for  removal.  But  it  is  some- 
times adopted  when  the  slag  is  to  be  used  for  filling  and  grading 


Operation  of  the  Furnace.  145 

purposes,  as  it  cools  in  small  masses  which  are  easily  broken.  As 
a  regular  practice  this  method  was  long*  ago  replaced  by  the  use 
of  cinder  cars,  some  of  which  are  still  used.  The  cars  had  a  cast 
iron  body  of  small  capacity  into  which  the  cinder  was  run,  and 
allowed  to  cool.  The  cakes  of  cold  cinder  were  then  hauled  to 
the  dump. 

The  almost  universal  practice  at  present  is  to  catch  the  molten 
cinder  in  large  ladles,  run  them  out  to  the  cinder  bank  and  empty 
them  before  solidification  takes  place.  For  this  purpose  the 
Weimer  cinder  ladle  has  long  been  the  standard  form.  It  consists 
of  a  large  plate  steel  riveted  pot,  securely  bolted  in  a  cast  steel  trun- 
nion ring,  and  lined  with  brick,  or  a  cast  iron  thimble  made  in 
one  piece  and  having  200  cubic  feet  capacity.  The  trunnion  is  sup- 
ported on  two  double  trucks  of  the  usual  railroad  pattern,  which 
are  connected  by  a  steel  cast  frame,  securely  riveted  to  buffers,  and 
having  standard  railroad  couplers  and  journal  boxes.  It  may  be 
tipped  to  either  side  by  means  of  worm  gear  operated  by  hand  or 
power. 

The  Pollock  cinder  ladle  is  constructed  on  similar  lines.  . 

The  Hartman  end-dump  cinder  car  has  been  less  generally 
used  than  the.  side-dump  type.     It  found  considerable  favor  be-    ™^7  1894 
cause  it  could  be  used  to  build  a  cinder  bank  forward  while  the   PV"**' 
other  cars  poured  to  the  sides.     It  has  a  semi-cylindrical  bowl 
which  is  lined  with  firebrick,  and  is  tilted  forward  by  means  of 
a  pole  attached  to  the  locomotive. 

Of  late  there  has  been  a  decided  tendency  toward  the  granula- 
tion of  cinder.  When  slag  is  allowed  to  run  into  a  brick  or  cement 
pit,  and  a  strong,  flat  stream  of  water  is  made  to  strike  the  stream 
of  slag  from  behind  as  it  falls,  the  slag  is  chilled  immediately  and 
falls  into  the  pit  in  a  granular  condition.  It  may  then  be  scooped 
out  by  means  of  a  clam-shell  or  orange-peel  bucket,  loaded  on 
cars  and  used  for  filling  or  road  material.  When  granulated  by 
water  at  a  pressure  of  80  to  100  pounds  per  square  inch,  slag 
makes  an  excellent  sand  for  mortar  and  concrete.  Granulation  in- 
creases the  volume  of  cinder  to  three  or  four  times  that  when 
molten,  and  hence  requires  greater  carrying  capacity.  It  also 
causes  a  great  volume  of  steam  in  the  cast  house  during  casting, 
which  is  a  decided  disadvantage. 


146  Blast  Furnace. 

The  relative  costs  of  handling  cinder  under  the  three  systems 
are  roughly  as  follows : 

In  gutters,  25  to  tfO  cents  per  ton  of  pig. 
In  ladles,  12  to  15  cents  per  ton  of  pig. 
By  granulation,  5  to  6  cents  per  ton  of  pig. 
Two-thirds  ton  cinder  to  a  ton  of  pig. 

The  quantity  of  cinder  and  slag  produced  by  a  blast  furnace 
is  generally  about  one  ton  for  every  two  of  iron  made.  Many 
attempts  have  been  made  to  utilize  this  vast  quantity  of  material, 
but  even  yet  the  greater  part  of  it  goes  over  the  clump.  It  is  said 
that  in  some  countries  bricks  can  be  made  of  slag  as  it  comes  from 
the  furnace,  but  the  tendency  of  good  cinder  to  slake  renders  that 
use  doubtful  in  the  United  States.  Cold  cinder  which  has  been 
broken  makes  excellent  railroad  ballast  or  filling,  and  is  a  suitable 
substitute  for  crushed  rock  in  making  concrete  or  roofing.  Gran- 
xSxr;  J.ISl  ulated  slag  mixed  with  50  per  cent,  slaked  lime,  moulded  and 
treated  with  steam  at  100  pounds  pressure  makes  satisfactory 
bricks.  Excellent  cement  is  made  by  mixing  crushed  granulated 
cinder  with  35  to  40  per  cent.  lime. 

Care  of  the  Notches — When  the  iron  flows  from  the  furnace 
evenly  and  not  too  rapidly,  it  is  usual  to  allow  the  blast  to  con- 
tinue, or  at  most  to  slacken  it  only  somewhat.  If  the  iron  comes 
more  rapidly  than  it  can  be  handled  to  advantage,  the  blast  must 
be  turned  off  entirely,  to  lessen  the  pressure  on  the  molten  ma- 
terials. When  the  flow  is  nearly  completed,  the  blast  is  put  on 
again,  in  order  that  the  additional  pressure  on  the  surface  of  the 
fluid  in  the  hearth  will  compel  more  of  it  to  flow  from  the  fur- 
nace. When  the  furnace  is  drained  as  much  as  is  practicable,  the 
tapping  hole  is  closed. 

There  are  two  general  methods  of  closing  the  tapping  hole. 
The  original  and  until  recent  years  the  universal  method  was  by 
means  of  balls  of  wet  clay  or  clay  mixed  with  10  to  20  per  cent, 
coal  or  coke  dust,  thrown  into  the  opening  by  a  helper  and  rammed 
back  by  a  stopping  hook  in  the  hands  of  the  keeper.  It  was  neces- 
sary to  throw  off  the  blast  completely  before  this  task  could  be 
attempted.  The  later  and  more  improved  method  consists  of 
using  a  large  pneumatic  or  steam  gun  to  shoot  clay  into  the  open- 


Operation  of  the  Furnace. 


147 


ing.  With  the  gun  it  is  usually  not  necessary  to  cut  off  the  blast 
completely.  The  Vaughn  gun,  which  is  universally  used,  con- 
sists of  two  cast  iron  cylinders,  which  are  connected  by  a  cast  iron 
distance  piece,  and  whose  pistons  are  joined  by  a  single  piston  rod. 
The  steam,  acting  upon  the  piston  in  the  steam  cylinder,  forces 


Iron  Age, 
Nov.  21,  1895. 


The  Vaughn  Gun. 


the  piston  in  the  mud  cylinder  to  eject  the  clay  on  every  stroke. 
The  gun  is  supported  by  a  pivoted  bracket,  by  which  it  may  be 
swung  into  place  and  clamped  before  discharging. 

When  the  shutting  of  the  tapping-hole  is  completed,  the  blast 
is  put  on  full  and  smelting  proceeds.  Iron  and  cinder  accumulate 
in  the  hearth.  After  about  two  hours,  the  cinder  arises  again  to 
the  tuyeres  and  must  be  flushed.  This  is  accomplished  by  simply 
drawing  the  plug  from  the  cinder  notch  and  allowing  the  cinder 


148  Blast  Furnace. 

to  run  until  it  is  drained  to  the  level  of  the  notch.  The  hole 
should  be  kept  free  during  flushing  by  means  of  a  pricker.  After 
the  first  flush  following  a  cast,  it  is  necessary  to  flush  again  as 
soon  as  the  cinder  rises  to  the  tuyeres.  The  period  is  much  shorter 
than  before,  owing  to  the  accumulated  iron  in  the  hearth.  A 
third  flush  and  perhaps  a  fourth  takes  place  before  tapping.  A 
sample  of  cinder  is  taken  every  flush,  in  a  way  similar  to  the  sam- 
ple of  iron.  It  is  needed  for  inspection  and  analysis.  Usually 
the  average  of  several  flushes  is  analyzed. 

CHARGING  THE   FCRNACE. 

When  the  furnace  has  been  filled  and  starts  on  its  career  of 
reduction  and  melting,  it  tends  to  empty  itself  rapidly  as  the  stock 
sinks.  Constant  vigilance  must  be  exerted  to  keep  a  full  column 
of  materials.  Proper  filling  and  distributing  of  stock  are  of  vital 
importance. 

Since  the  furnace  charges  must  be  determined  beforehand,  and 
used  in  the  proportions  thus  predetermined,  it  is  necessary  that 
the  different  kinds  of  stock  should  be  carefully  weighed.  The 
stock  house  must  therefore  be  provided  with  suitable  scales,  ^he 
use  of  a  multiple  beam  scale  is  universal.  This  enables  a  separate 
beam,  properly  counterweighted,  to  be  set  aside  for  each  kind  of 
stock,  and  the  weigher  has  only  to  see  that  each  barrow  balances 
on  the  proper  beam  before  sending  it  up. 

The  basis  of  the  furnace  charge  is  the  weight  of  fuel  in  each 
"  round."  Usually  a  definite  number  of  pounds  of  fuel,  varying 
from  4,800  to  14,000,  according  to  the  capacity  of  the  furnace, 
is  taken  as  the  basis  of  the  round  and  this  quantity  remains 
fixed.  The  proportions  of  ore  and  stone,  however,  are  variable. 
The  ore  is  varied  according  to  the  heat  development  in  the 
hearth  of  the  furnace,  and  the  stone  is  varied  according  to  the 
requirements  of  the  ore  and  fuel.  The  usual  order  of  dumping 
is  to  put  the  charge  of  fuel  in  the  first  hopper ful,  and  the  ore 
and  then  the  stone  in  the  second.  In  the  case  of  furnaces  which 
are  filled  automatically  by  means  of  a  self-dumping  skip,  the 
skip  is  so  large  that  four  skipfuls  constitute  a  round.  In  the 


Operation  of  the  Furnace.  149 

case  of  hand-filled  furnaces,  however,  the  weight  on  a  stock 
buggy  must  not  exceed  the  power  of  the  man  who  handles  it. 
Hand  buggies,  therefore,  usually  carry  1,000  to  1,800  pounds  of 
stock.  Coke  is  so  light  that  it  is  customary  to  have  larger 
buggies  in  order  that  too  many  may  not  be  needed.  A  coke 
buggy  rarely  carries  over  960  pounds  and  the  number  needed 
to  constitute  a  round  will  vary  from  6  to  12,  according  to  the 
size  of  round  adopted.  It  is  usual  to  distribute  the  ore  charge 
through  an  equal  number  of  the  smaller  ore  buggies,  and  half 
that  number  of  buggies  will  suffice  to  hold  the  limestone.  Usually 
the  number  of  buggies  to  the  round  is  kept  constant,  any  varia- 
tion in  the  furnace  charge  being  made  by  varying  the  weight  of 
ore  and  stone  in  each  buggy.  Since  the  multiple-beam  scale 
permits  the  devotion  of  a  separate  beam  to  each  kind  of  stock, 
and  the  counterweight  may  be  clamped  to  the  beam  and  the 
beam  box  locked,  the  weigher  needs  no  discretion  beyond  select- 
ing the  right  beam  and  seeing  that  the  proper  number  of  buggies 
to  the  charge  goes  up  promptly. 

In  the  case  of  automatically  charged  furnaces  which  are 
provided  with  stock  distributors,  the  weighing,  hoisting  and 
dumping  of  the  charges  are  in  the  hands  of  one  or  two  men 
who  operate  from  the  stock  house.  In  the  case  of  hand-filled 
furnaces,  the  stock  is  brought  to  the  scales  by  the  bottom- 
fillers,  weighed,  run  on  the  hoist,  and  sent  to  the  top  of  the 
furnace,  where  it  becomes  the  care  of  the  top-fillers.  The  top 
fillers  run  the  buggies  to  the  hopper  and  dump  them  around 
the  bell.  After  each  round  or  definite  fraction  thereof  has 
been  dumped,  the  bell  is  lowered  and  the  stock  slides  into  the 
furnace. 

Stock  Distribution — The  proper  distribution  of  the  stock 
around  the  hopper  is  essential  to  a  well-working  furnace.  In  the 
case  of  automatic  distributors,  the  distribution  depends  upon  the 
type  of  distributor  used.  In  the  case  of  hand-dumping,  the 
distribution  depends  upon  the  top  fillers.  It  should  not  be  left  to 
their  discretion,  but  a  definite  system  of  dumping  should  -be 
adopted  and  rigidly  followed.  The  basis  of  proper  dis- 
tribution is  symmetry.  The  hopper  should  be  divided 


150  Blast  Furnace. 

into  a  definite  number  of  dumping  stations,  as  four,  six. 
or  eight ;  the  charges  sent  up  in  a  definite  and  constant  order, 
and  dumped  symmetrically.  If  the  first 
four  buggies  of  coke  are  dumped  at  i,  3,  5, 
and  7,  the  next  four  should  be  at  2,  4,  6, 
and  8.  If  stone  be  dumped  first  at  2  and 
6,  let  the  next  be  at  4  and  8.  If  one  buggy 
of  mill  cinder  goes  in  each  round,  let  it  be 
dumped  in  a  spiral  form,  i,  2,  3,  4,  5,  6,  7,  8, 
thus  giving  symmetrical  distribution. 

As  we  shall  see  later,  the  less  the  height  of  the  column  of 
materials  within  certain  limits,  the  greater  the  need  of  fuel  to 
maintain  full  furnace  temperature.  It  is  imperative  therefore 
that  the  furnace  should  be  kept  full  to  the  stockline,  leaving  only 
room  enough  for  the  proper  manipulation  of  the  bell.  It  is  the 
duty  of  the  top  fillers  to  watch  the  height  of  the  stock  by  gauging 
it  at  intervals.  This  consists  of  measuring  the  distance  to  the 
stock  by  means  of  an  iron  rod,  thrust  in  turn  through  four  small 
equidistant  holes  left  for  the  purpose  around  the  hopper  in  the  fur- 
nace top.  The  stock  should  be  gauged  at  all  four  points  in  order 
to  discover  whether  it  descends  evenly  over  the  whole  area  of 
the  furnace.  Irregularity  of  descent  may  not  be  detected  by 
observing  the  same  spot  constantly. 

OPERATION  OF  STOVES. 

The  care  of  hot  blast  stoves  should  never  be  trusted  to 
unskilled  hands,  as  thereby  much  damage  may  be  done.  In 
changing  stoves,  which  is  usually  done  every  hour,  the  new  one 
must  be  put  on  blast  before  the  old  one  is  taken  off,  in  order 
that  the  blast  may  be  continuous.  In  order  to  put  the  blast  into 
a  stove  which  is  burning  gas,  it  is  necessary  first  to  shut  off  the 
gas  and  to  close  the  gas  and  air  ports,  and  also  the  valve  to  the 
chimney,  thus  making  the  stove  perfectly  tight.  Then  the  cold 
blast  valve  should  be  opened  very  gently  until  the  stove  is  filled 
with  the  blast.  This  is  done  in  order  that  the  temporarily  in- 
creased outlet  for  the  blast  may  not  cause  the  blowing  engine 


Operation  of  the  Furnace.  151 

to  race.  The  hot  blast  valve  may  then  be  opened  and  we  have 
two  stoves  on  blast.  The  old  stove  may  then  be  taken  off  in 
practically  the  reverse  order.  The  hot  blast  valve  is  closed  first, 
then  the  cold  blast  valve.  The  trapped  blast  must  then  be  let  out 
by  cautiously  opening  an  air  port.  When  the  pressure  is  relieved, 
the  chimney  valve  and  then  the  gas  valve  is  opened,  and  the  air 
ports  regulated  to  suit  conditions. 

When  the  blast  is  off  the  furnace,  no  gas  comes  through 
the  downtake  to  the  stoves.  Meanwhile  the  chimney  is  drawing 
cold  air  through  the  stoves  on  gas  and  robbing  them  of  their 
heat.  Hence  the  gas  and  air  inlets  should  be  closed  whenever 
the  blast  stops.  If  the  stop  is  to  be  of  considerable  duration, 
the  chimney  valves  should  be  closed  and  everything  made  tight. 
The  hot  and  cold  blast  valves  of  the  stove  in  use  should  be 
closed  also. 

If  a  stove  gets  cold  through  over  use  or  from  any  other 
cause,  and  is  not  hot  enough  to  ignite  the  gas  upon  its  entrance, 
burning  wood  or  waste  should  be  placed  in  the  combustion 
chamber  to  insure  ignition  and  prevent  explosion.  The  quantity 
of  gas  that  may  be  burned  in  a  stove  is  ordinarily  all  that  can  be 
spared  from  the  boilers.  It  will  vary  with  the  kind  of  gas.  The 
air  ports  must  be  regulated  to  satisfy  the  requirements  of  the 
gas  in  order  to  bring  about  complete  combustion.  Any  excess  of 
gas  passes  through  the  stove  unconsumed,  and  any  excess  of 
air  passes  through  unchanged.  In  either  case  no  heat  is  given  up 
to  the  stove  but  some  is  taken  away,  since  any  useless  excess  of 
either  absorbs  heat  and  carries  it  out  of  the  stove. 

Cleaning  the  Stove. — Dust,  which  is  brought  to  the  stoves  by 
the  gases,  wall  accretions,  pieces  of  brick,  etc.,  fall  and  accumu- 
late in  the  bottom  of  the  combustion  chamber  in  a  more  or  less 
fused  condition.  It  is  necessary  that  the  cleaning  doors  should 
be  opened  and  this  dirt  removed  every  few  days.  Some  of  the 
dust  is  also  carried  up  through  the  combustion  chamber,  falls 
through  the  checkers,  accumulates  in  the  chambers  beneath,  and 
gradually  chokes  up  the  passages.  At  least  once  a  month  all  of 
the  cleaning  doors  should  be  opened  to  scrape  this  dirt  out.  Semi- 
fused  incrustatons  adhere  to  the  top  of  the  checker  flue  walls, 


152  Blast  Furnace. 

where  they  gradually  bridge  across  and  stop  the  flues.  Such 
accumulations  should  be  removed  at  least  every  six  months,  by 
letting  the  stove  cool  down  and  opening  the  cleaning  doors 
on  the  top. 

INTERRUPTIONS    IN    WORKING. 

When  once  blown  in,  a  furnace  usually  continues  in  blast 
for  some  years,  until  some  portion,  generally  the  lining,  is  dam- 
aged beyond  repair,  when  it  is  "  blown  out."  There  are,  how- 
ever, two  forms  of  temporary  interruption,  known  respectively  as 
"  banking  "  and  "  blowing  down." 

Banking  the  Furnace. — It  is  frequently  desirable  to  suspend 
temporarily  the  operation  of  a  furnace,  owing  to  lack  of  sup- 
plies, labor  troubles,  extensive  repairs,  etc.  In  such  cases  the  fur- 
nace is  "  banked  "  by  stopping  the  blast  and  smothering  the  fire  by 
filling  with  clay  all  openings  which  would  admit  air  to  support 
the  combustion  of  the  fuel.  During  the  period  when  the  furnace 
is  banked,  it  will  lose  heat  by  radiation,  in  cooling  water,  etc., 
which  will  leave  a  deficiency  of  heat  in  the  hearth  when  the 
blast  is  put  on  again.  To  provide  against  this  deficiency  it  is 
necessary  to  precede  the  stop  by  a  large  blank  of  coke,  followed 
by  light  charges  of  ore  not  exceeding  one-half  to  two-thirds 
normal,  depending  upon  the  length  of  the  stop  expected.  The 
longer  the  stop  is  to  be,  the  larger  should  be  the  coke  blank  and 
the  lighter  the  subsequent  charges  of  ore.  At  the  same  time,  a 
blanket  of  fine  ore  spread  over  the  top  of  the  stock  tends  to 
seal  the  body  and  prevent  draught.  As  soon  as  the  coke  blank 
has  reached  the  bosh,  the  blast  should  be  taken  off  and  the 
furnace  tapped  clear  of  iron  and  cinder  so  that  there  will  be 
nothing  left  to  solidify.  The  tuyeres  and  cinder  notch  are  then 
removed,  the  openings  bricked  up  and  every  crevice  from  the 
mantle  down,  luted  with  clay  and  the  gas  burners  of  the  stoves 
and  boilers  closed  to  prevent  draught.  In  spite  of  these  precau- 
tions, some  combustion  will  take  place  and  the  stock  will  sink 
in  the  furnace.  On  starting  up  again,  it  is  advisable  to  fill  with 
coke  the  space  due  to  settling,  and  then  to  start  light,  but 
gradually  increasing,  charges  of  ore. 


Operation  of  the  Furnace.  153 

The  history  of  a  successful  banking  charge  of  an  80  X    15 
foot  furnace,  making  basic  iron,  was  as  follows : 

Fuel  blank 165,000  pounds  coke. 

Flux   , 32,500  pounds  limestone. 

f  27,500  pounds  coke. 

Charge {  28,000  pounds  ore. 

[  12, 000  pounds  stone. 

Blanket  24,000  pounds  fine  ore. 

f  27,500  pounds  coke. 

Charge {  28,000  pounds  ore. 

[  12,000  pounds  stone. 

Fuel  blank 27,500  pounds  coke. 

Blanket 24,000  pounds  fine  ore. 

The  furnace  was  banked  ten  weeks,  during  which  the  stock 
settled  20  feet,  an  average  of  2  feet  per  week.  This  space  needed 
66,000  pounds  coke  to  fill  it  and  that  weight  represents  approxi- 
mately the  amount  of  coke  burned  in  ten  weeks,  through  infiltra- 
tion of  air.  When  the  furnace  was  opened  up,  at  the  end  of 
ten  weeks,  the  crucible  was  full  of  ashes  and  good  coke  was 
before  the  tuyeres.  The  ashes  were  raked  out  through  both 
notches  and  the  notches  closed,  the  tuyeres  put  in  and  the  blast 
put  on.  The  first  cinder,  flushed  6  hours  later,  was  hot  and 
gray,  having  31.2  per  cent.  SiO2  and  19.8  per  cent.  A12O3.  The 
first  iron  was  tapped  at  the  end  of  24  hours,  and  was  high  in 
silicon  and  sulphur,  having  Si.,  2.26  per  cent,  and  S.,  0.386  per 
cent.  On  the  fourth  cast  the  analysis  was  Si.,  0.88  per  cent  and 
the  S.,  0.049  Per  cent-  By  the  sixth  day  the  furnace  was  in 
normal  condition,  making  iron  that  averaged  Si.,  0.80  per  cent 
and  S.,  0.028  per  cent.,  and  cinder  that  averaged  SiO2,  33.1  per 
cent,  and  A12O3,  13.8  per  cent. 

If  the  suspension  is  expected  to  last  only  a  few  days,  the 
coke  blank  may  be  reduced  to  a  half  or  three  quarters  of  the 
above  amounts,  but  the  other  details  may  be  practically  identical. 
When  the  exigency  is  so  sudden  that  time  is  not  given  to  prepare 
the  furnace  for  a  stop,  the  only  course  is  to  remove  the  tuyeres 
and  cinder  notch  and  plug  all  the  openings  at  once.  Before 
starting  up,  however,  it  is  advisable  to  open  the  notches  and  take 
time  to  cut  through  all  chilled  material  to  clean  stock  and  to 
fill  the  openings  with  a  mixture  of  sand  and*  fire  clay.  This 
precaution  will  ensure  the  ready  opening  of  the  notches  when 
needed.  If  it  is  found  that  a  solid  crust  has  formed  across  the 


154  Wast  Furnace. 

hearth  beneath  the  tuyeres,  the  explosion  of  a  few  sticks  of 
dynamite  in  the  centre  of  the  hearth  will  break  up  the  crust  so 
that  molten  material  may  reach  the  bottom.  If  this  precaution 
is  neglected,  it  may  be  necessary  to  tap  the  iron  through  the 
cinder  notch  for  several  days. 

When  the  blast  is  put  on  and  charging  begins,  a  coke  blank, 
followed  by  light  charges  should  be  used  first,  in  order  that  the 
hearth  may  have  an  opportunity  to  regain  its  lost  heat  as  soon 
as  possible.  For  a  furnace  80  X  15  feet,  a  coke  blank  of  30,000 
pounds  should  be  used,  followed  by  ten  charges  of  ore,  which 
are  about  one-third  normal.  This  should  be  followed  by  another 
coke  blank  of  20,000  pounds,  upon  which  gradually  increasing 
charges  may  be  built  up,  as  before. 

Blowing  Down. — When  a  furnace  is  going  out  of  blast  and 
also  in  some  instances  of  irregular  working,  charging  is  stopped 
and  the  stock  is  allowed  to  settle  with  gradually  decreasing  blast. 
This  phase  of  operation  is  termed  "  blowing  down."  When 
blowing  down  is  merely  a  corrective  measure,  it  rarely  proceeds 
as  far  as  the  bosh  before  its  purpose  has  been  accomplished.  As 
the  charges  sink  without  the  addition  of  cold  stock,  the  top  of 
the  furnace  gets  hot  and  explosions  are  very  liable  to  occur. 
To  keep  the  top  cool  and  to  prevent  warping  the  bell  or  hopper, 
some  method  of  cooling  is  necessary.  The  most  satisfactory  way 
is  to  use  sprays  of  water,  and  to  keep  the  temperature  between 
500  and  600  degrees  F.  This  is  done  by  using  perforated  inch 
pipes  inserted  in  the  furnace  top  through  the  four  gauge  holes 
and  projecting  to  a  depth  of  5  feet  below  the  bell.  The  finer  the 
sprays,  the  greater  is  their  efficiency.  The  refilling  of  the  furnace 
should  be  preceded  by  a  coke  blank,  followed  by  light  charges 
as  before. 

Blowing  Out — When  conditions  are  such  that  it  is  desirable 
to  end  the  campaign  of  a  furnace,  the  furnace  is  "  blown  out." 
The  first  phase  of  blowing  out  a  furnace  is  identical  with  blowing 
down.  As  the  stock  sinks,  sprays  of  water  are  used  to  keep  the 
top  cool.  As  the  body  of  material  gets  thinner  and  lighter,  the 
pressure  of  the  blast  is  lessened.  The  blast  may  continue  until 
the  top  of  the  stock  is  within  a  few  feet  of  the  tuyeres,  when 
it  is  necessary  to  stop  because  even  a  light  blast  will  blow  the 


Operation  of  the  Furnace.  155 

stock  about  in  the  empty  furnace  without  any  further  advantage. 
When  the  blast  is  finally  stopped,  all  of  the  tuyeres  and  coolers 
are  removed  from  the  furnace,  the  remnants  of  the  stock  are 
raked  out  of  the  hearth  and  the  furnace  is  ready  to  be  dismantled 
for  repairs. 


CHAPTER  IV. 

BURDENING  THE  FURNACE. 

The  Furnace  Burden — The  ratio  of  the  ore,  with  its  accom- 
panying flux,  to  the  fuel  of  a  furnace  charge  is  generally  termed 
the  "  burden  "  of  the  furnace.  The  task  of  determining  the 
quantity  of  each  which  is  best  suited  to  furnace  conditions  is 
designated  as  "  burdening  the  furnace."  The  successful  running 
of  a  furnace  probably  depends  more  upon  proper  burdening  than 
upon  any  other  single  factor  in  its  management.  In  the  early  days 
of  the  industry,  before  the  constant  application  of  chemical 
analysis  to  the  materials  used,  burdening  was  a  combination  of 
previous  experience  and  guesswork.  If  any  raw  material  from 
an  unfamiliar  source  had  to  be  used,  the  treatment  required  had 
to  be  guessed  until  it  could  be  determined  by  experience.  With 
the  application  of  analytical  methods,  however,  it  became  possible 
to  predict  with  tolerable  accuracy  the  requirements  of  any  ma- 
terials from  their  chemical  compositions. 

Furnace  Control — The  constant  care  of  the  furnaceman  must 
be  centered  chiefly  upon  two  aims ;  to  keep  the  furnace  working 
freely,  and  to  maintain  a  satisfactory  product.  The  two  variables 
at  his  command,  by  which  he  must  achieve  results,  are  heat  and 
slag  composition.  With  sufficient  heat  and  properly  composed 
slags  a  wide  range  of  products  may  be  obtained  from  identical 
materials.  The  proper  amount  of  heat  in  the  furnace  is  that 
which  will  maintain  the  least  temperature  necessary  to  perform 
the  work  desired.  Any  excess  is  waste.  The  temperature  which 
is  necessary  to  attain  given  results  depends  upon  the  kind  of 
product  desired,  and  is  inseparably  linked  with  the  slag  composi- 
tion. Generally  speaking,  the  slag  is  the  substance  that  requires 
the  highest  temperature  for  its  proper  disposal,  and  when  that 
temperature  has  been  attained  it  is  ample  for  all  other  considera- 
tions. The  amount  of  heat  needed  for  the  proper  behavior  of 
slag  is  dependent  chiefly  upon  the  slag  composition. 

156 


Burdening  the  Furnace.  157 

SLAG. 

By  the  uninitiated,  slag  is  too  often  looked  upon  as  a  highly 
undesirable,  but  quite  unavoidable  excoriation  from  metallurgical 
processes.  The  proper  mental  attitude  toward  a  slag  is  to 
consider  it  a  reagent  divinely  appointed  for  the  purification  of 
metals.  Since  in  any  metallurgical  process,  all  of  the  non-volatile 
constituents  must  appear  in  either  the  metal  or  the  slag,  it  follows 
that  whatever  we  would  eliminate  from  the  metal  must  be 
accommodated  in  the  slag.  This  result  can  be  accomplished  only 
by  giving  to  the  slag  such  a  character  that  it  will  offer  to  the 
impurity  a  stronger  attraction  than  is  offered  by  the  metal. 

Slag  Constitution. — The  cardinal  difference  between  a  metal 
and  a  slag  determines  whether  a  given  particle  shall  enter  the 
one  or  the  other.  This  difference  lies  in  the  fact  that  the  slag- 
is  composed  essentially  of  elements  which  are  oxidized,  while 
the  metal  admits  them  only  when  in  the  elemental  condition. 
Silicon,  manganese,  phosphorus,  sulphur,  and  iron  may  exist 
simultaneously  in  both  slag  and  metal.  In  the  slag,  silicon  will 
exist  only  as  SiO2,  but  in  the  metal  as  Si.  In  the  same  way,  all 
of  the  MnO,  P2O5,  SO2  and  FeO  will  be  found  in  the  slag,  while 
the  metal  will  be  found  to  contain  elemental  Fe,  Mn,  P  and 
S.  Since  all  the  elements  are  in  the  condition  of  oxides  when 
they  enter  the  furnace,  it  follows  that  they  can  be  found  in  the 
metal  only  after  they  have  lost  their  oxygen.  Any  elements, 
however,  which  are  not  deoxidized  by  the  action  of  the  blast 
furnace  can  therefore  never  be  found  in  pig  iron.  This  is  why 
Ca,  Mg,  Al  and  alkalis  are  always  absent  from  pig  iron  although 
present  in  the  furnace  in  abundance. 

Blast  furnace  slags  consist  primarily  of  calcic  silicate, 
although  either  the  lime  or  the  silica  may  be  partially  replaced 
by  other  radicals.  The  lime  is  often  partly  replaced  by  magnesia, 
and  generally  by  small  quantities  of  the  oxides  of  iron,  manganese 
and  the  alkalis.  The  silica  is  always  accompanied  by  alumina, 
and  also  by  sulphur,  either  in  the  oxidized  or  elemental  condi- 
tion. The  vast  majority  of  blast  furnace  slags  to-day  will  fall 
between  the  following  limits  in  composition : 


158  Blast  Furnace. 


SiO3 

Per  cent. 
25  to  50 

MnO 

Per  cent. 
Tr  to    '•* 

5  to  20 

K20      I 

Tr  tn    1 

CaO   
MgO    

25  to  50 
,  Tr.  to  25 

Na2O    j  *  ' 

g 

Tr  to    2 

FcO   

Tr.  to    1 

P    . 

.  .Tr. 

While  it  is  probable  that  there  are  at  least  traces  of  all  of 
the  above  constituents  in  every  blast  furnace  slag,  yet  all  but 
the  first  three  might  be  absent  without  interfering  in  the  least 
with  its  functions. 

Slag  Function — The  function  of  the  slag  is  the  removal  from 
the  furnace  of  any  non-volatile  matter  that  does  not  properly 
belong  in  the  pig  iron.  We  have  seen  that  the  alumina  and  all 
of  the  earthy  and  alkaline  bases  naturally  enter  the  slag,  and 
that  they  are  accompanied  by  the  bulk  of  the  silica  and  sulphur. 
If  we  neglect  for  the  moment  the  unavoidable  traces  of  iron  or 
manganese,  it  becomes  evident  that  the  only  variables  in  this  list 
are  the  silica  and  sulphur,  and  it  is  in  respect  to  these  two  that 
the  functions  of  the  slag  are  chiefly  manifested.  The  removal 
of  the  sulphur  and  the  regulation  of  the  silicon  in  pig  iron  are 
tasks  which  devolve  largely  upon  the  slag. 

A  suitable  blast  furnace  slag  is  always  characterized  by 
perfect  fluidity  at  furnace  temperatures.  All  constituents  must 
be  in  complete  fusion  so  that  all  the  fluxing  power  will  be  exerted 
to  the  utmost  and  in  order  that  the  slag  may  be  readily  drained 
from  the  furnace.  Such  a  slag  will  have  a  quiet,  rapid  flow  with- 
out froth  or  viscosity.  "  Hot,  fluid  and  gray  "  is  a  time-worn 
description  of  good  slag  which  still  holds  true. 

Slag  Efficiency — The  efficiency  of  slag  in  controlling  the 
quantity  of  silicon  and  sulphur  in  pig  iron  depends  upon  its  ability 
to  take  up  and  retain  these  two  elements.  This  ability  in  turn 
depends  upon  the  basicity  of  the  slag.  Properly  speaking,  the 
term  "  basicity  "refers  to  the  proportion  of  bases  in  a  compound, 
but  in  the  case  of  the  blast  furnace  slag  the  basicity  is  usually 
reckoned  in  terms  of  the  acid  constituents — viz.,  silica  and 
alumina.  That  is  to  say,  it  is  the  custom,  as  a  rule,  to  watch  the 
percentage  of  silica  and  alumina  in  the  slag  from  day  to  day, 
and  to  disregard  the  percentage  of  bases.  The  result  is  the 


Burdening  the  Furnace.  159 

same  in  the  end,  however,  for  whatever  is  not  acid  in  the  slag 

must  be  base. 

Slag  Composition.— While  the  SiO2  and  A12O3  together  are 
usually  considered  as  the  acid  constituents  of  the  slag,  they  are 
not  by  any  means  co-ordinate.  SiO2  is  always  a  strong,  definite 
acid,  no  matter  where  it  is  found.  A12O3,  on  the  other  hand,  is 
more  often  found  acting  as  a  base.  It  unites  with  all  acids  to 
form  aluminic  salts  much  as  other  bases  do.  It  even  unites  with 
SiO.,  itself  to  form  clay,  an  aluminic  silicate,  in  which  it  performs 
unaided  all  the  duties  of  a  base.  But  in  the  presence  of  other 
more  positive  bases  and  particularly  when  there  is  a  deficiency 
of  acid  constituents,  the  dual  nature  of  A12O3  is  manifested,  and 
it  cooperates  to  supply  the  deficiency.  It  is  under  these  conditions 
that  it  exists  in  the  blast  furnace  slag,  which  may  be  considered 
usually  a  tolerably  basic  compound.  The  power  of  A12O3  to 
act  as  a  substitute  for  SiO2  in  slags  is  forcibly  illustrated  by  the 
ease  with  which  highly  aluminous  slags  give  up  silicon  for  reduc- 
tion and  incorporation  with  the  pig. 

Acid  Constituents — The  united  percentages  of  SiO2  and 
A12O3  in  the  blast  furnace  slag  usually  range  between  40 
and  50  per  cent,  of  the  whole,  though  occasionally  higher. 
They  cooperate  with  such  harmony  that  the  A12O3  ranges  quite 
generally  from  5  to  20  per  cent,  without  materially  altering  the 
nature  of  the  compound.  It  has  been  shown  by  Howe  that  in  all 
silicates,  ranging  from  subsilicates  to  trisilicates,  in  which  the 
lime  ranges  from  30  to  45  per  cent.,  substituting  A12O3  for  SiO 
does  not  materially  affect  the  heat  of  formation.  It  should  not  18fl«- 
be  understood,  however,  that  the  resemblance  is  exact.  As  would 
be  naturally  expected  from  its  neutral  nature,  the  substitution  of 
A12O3  for  SiO2  without  altering  the  bases,  will  give  a  slag 
of  more  limey  appearance  and  greater  basic  power  for  the  same 
total  acids,  than  a  higher  proportion  of  SiO2  to  A12O3  would 
give,  yet  without  undue  refractoriness.  When  A12O3  is  in  excess 
of  SiO2,  their  combined  amount  may  rise  to  60  per  cent,  without 
losing  the  characteristics  of  a  basic  slag.  On  the  other  hand  a 
highly  aluminous  slag,  which  is  deficient  in  bases  will  not  reveal 
its  acid  properties  so  markedly  as  when  the  proportion  of  SiO2 
is  higher.  It  is  said,  however,  that  the  substitution  of  20  per 


2     Tr.A.  I.  M.  E., 


160  Blast  Furnace. 

cent.  MgO  for  an  equivalent  quantity  of  lime  will  produce 
viscosity  in  slags  having  over  10  per  cent.  A12O3. 

As  a  rule  SiCX  +  A12O3  amounts  to  45  to  48  per  cent,  of  the 
slag,  of  which  about  one-third  is  A12O3  and  two-thirds  SiCX. 
The  percentage  of  the  slag  which  they  represent  is  regulated  by 
the  proportion  of  stone  used  for  flux.  The  ratio  which  they  bear 
to  each  other,  howrever,  depends  upon  their  original  proportions 
in  the  materials  of  the  charge,  which  cannot  be  easily  regulated. 
In  the  majority  of  ores  the  proportion  of  A12O3  to  SiCX  in  the 
gangues  is  about  I  to  4  or  5.  The  ash  of  the  coke,  however, 
being  generally  of  slaty  composition,  and  therefore  akin  to  clay, 
is  generally  high  in  A12O3.  This  fact,  coupled  with  the  removal 
of  SiO2  through  deoxidation,  accounts  for  the  final  ratio  of  i  to 
2  in  the  slag.  Some  average  ratios  of  SiO2  to  A12O3  in  slags  made 
from  ores  of  different  localities  in  United  States  are  given  below : 

Ratio  of 

Locality.                                        SiO2.  AlaOs.  SiO2  +  A12O3.   SiO2  to  A12O3. 

Lake  ores,  P.  S.  Co 30  17  47                       1.8 

Lake  ores,  C.  I.  &  S.  Co 32  14  46                       2.3 

Cornwall    ore 34  15  49                       2.3 

Alabama  ore 35  15  50                       2.3 

Virginia    ore 38                     9.5  47.5  4.0 

In  addition  to  the  SiO2  and  A12OS,  sulphur  acts  as  an  acid 
radical  and  unites  with  lime  to  form  CaS.  It  is  probable  that 
this  union  cannot  occur  except  in  the  presence  of  carbon  or 
other  reducing  agent,  which  can  unite  with  the  oxygen  given 
up  by  the  lime  as  in  the  following  reaction: 

CaO  +  C  +  S  =  CaS  +  CO. 

Each  per  cent,  of  sulphur  neutralizes  1.25  per  cent  of  Ca  in  the 
slag,  and  the  calcic  sulphide  so  formed,  exists  dissolved  in  the 
silicate  of  the  slag.  The  quantity  of  sulphur  in  the  slag  ranges 
usually  from  I  to  2  per  cent.  The  solubility  of  the  sulphide  in 
slags  is  low,  hence  but  little  is  dissolved  and  it  separates  readily. 
The  solubility  increases  with  temperature  and  basicity.  The 
presence  of  sulphur  in  iron  and  slag  simultaneously  may  be 
looked  upon  as  a  two-phase  solution,  and  the  distribution  of 
sulphur  between  the  two  phases  depends  upon  the  composition  of 
each.  The  coefficient  of  solubility  in  slags  is  increased  by 
basicity,  and  that  in  iron  by  the  presence  of  carbon  and  manga- 


Burdening  the  Furnace.  161 

nese.     Evidently,  therefore,  absolute  desulphurization  of  iron  by 
slag  is  impossible. 

Basic  Constituents — The  other  half  of  the  slag  is  made  up  of 
bases.  The  ratio  of  bases  to  acids  in  slags  usually  ranges  from 
i  to  1.3,  although  these  limits  are  often  exceeded.  In  a  large 
percentage  of  successful  slags,  the  sum  of  the  earthy  bases 
(CaO-}- MgO)  approximately  equals  the  sum  of  the  acids 
(SiO2  +  A12O3),  each  being  about  47  per  cent.,  while  the 
remaining  5  or  6  per  cent,  is  made  up  of  CaS,  alkalies  and 
oxides  of  the  heavy  metals.  The  latter,  however,  under  normal 
working,  are  fixed  by  the  unalterable  conditions  of  the  problem 
at  each  furnace,  and  are  not  subject  to  material  manipulation. 
The  proportions  of  the  earthy  bases,  on  the  other  hand,  are  under 
strict  control  and  may  be  subjected  to  considerable  variation. 
While  the  ratio  of  CaO  to  MgO  in  the  slag  may  be  affected  to 
some  extent  by  the  composition  of  the  gangue  and  the  ash,  it  is 
mainly  dependent  upon  their  ratio  in  the  flux  used.  Some  lime- 
stones are  practically  free  from  magnesia  and,  in  consequence, 
the  slags  which  result  will  carry  very  little  MgO.  On  the  other 
hand,  magnesian  limestones  are  much  used  for  flux  in  some 
localities.  A  pure  dolomite  contains  30.43  per  cent.  CaO  and 
21.74  MgO,  a  ratio  of  1.4  to  I,  which  is  about  the  maximum 
ever  found  in  slags.  It  must  be  remembered,  however,  that  MgO 
has  a  fluxing  power  1.4  times  that  of  CaO,  which  brings  them  on 
a  parity  in  efficiency  when  in  such  proportions.  Generally  the 
percentage  of  MgO  in  blast  furnace  slags  does  not  fall  far  below 
5  per  cent,  and  rarely  goes  much  above  20  per  cent.  Under 
ordinary  conditions  it  may  vary  between  these  limits  without 
affecting  materially  the  quality  of  the  slag.  As  a  rule  the  addition 
of  MgO  to  calcareous  slags  lowers  the  melting  points,  since  poly- 
basic  silicates  are  usually  more  fusible  than  silicates  of  a  single 
base.  With  tolerably  pure  silicate  slags,  having  less  than  5  per 
cent.  A12O3,  the  proportion  of  MgO  need  be  of  little  concern, 
since  successful  slags  have  been  run  with  CaO  as  low  as  12  per  T.-.A.  i.  M.  E., 
cent.  If  A12O3  exceeds  10  per  cent.,  however,  MgO  in  excess  of  XXIV^p>49& 
20  per  cent,  causes  too  much  viscosity  in  the  cinder,  whereby  it 
becomes  sticky  and  does  not  work  freely. 

Fusibility  of  Slags — Slags  may  best  be  regarded  as  mutual 


162  Blast  Fur  mice. 

• 

solutions  of  various  oxides,  and  it  is  necessary  for  the  more 
fusible  components  to  fuse  in  order  to  dissolve  the  less  fusible. 
For  this  reason  the  temperature  of  the  formation  of  slag  is 
generally  higher  than  its  melting  point.  The  finer  the  state  of 
division,  and  the  more  intimate  the  mixture,  the  nearer  these 
temperatures  approach.  Experiments  by  Boudouard  upon  the 
melting  points  of  various  mixtures  illustrate  the  mutual  effect 
of  different  components  upon  each  other.  He  places  the  melting 
point  of  SiO2  at  3325  degrees  F.,  and  states  that  the  addition  of 
A12O3  lowers  the  melting  point.  The  minimum  is  reached  with 
15  per  cent.  A12O3,  which  melts  at  3075  degrees  F.  Further 
addition  of  A12O3  causes  a  rise  of  melting  point.  46  per  cent. 
inst.  Jour.,  ALO3  and  54  per  cent.  SiO2  melts  at  the  same  temperature  as 
pure  SiO2.  Al2O3SiO2  melts  at  3435  degrees  F.  and  pure  ALO3 
probably  melts  far  above  3600  degrees  F. 

The  addition  of  CaO  to  SiO2  lowers  the  melting  point  rapidly. 
30  per  cent.  CaO  brings  the  melting  point  below  2730  degrees  F., 
40  per  cent,  gives  the  minimum  melting  point,  2650  degrees  F. 
Further  addition  of  CaO  causes  the  melting  point  to  rise  gradually 
but  irregularly,  till  at  90  per  cent.,  it  is  again  2730  degrees  F. 

The  addition  of  13  per  cent.  A12O3  to  CaO  gives  a  melting 
point  of  2640  degrees  F.,  55  per  cent,  A12O3  gives  the  lowest 
melting  point,  2540  degrees  F.  Above  60  per  cent.  A12O3  the 
melting  point  rises  rapidly  to  that  of  pure  A12O3. 

The  following  analyses  by  the  same  author  show  how  little 
the  melting  point  is  affected  by  considerable  changes  in  CaO 
and  SiO2: 

Melts  at 
SiO2.  CaO.  degrees  P. 

62.0  38.0 2,590 

51.8  48.2 2,625 

34.8  65.2 2,660 

21.2  78.8 2,660 

The  addition  of  A12O3  to  such  a  lime  silicate,  however, 
lowers  the  meeting  point  materially,  thus : 

Mel  ting  point, 
SiO2.  A12O3.  CaO.  degrees  F. 

34.8  0.0  65.2 2,660 

37.4  10.3  52.3 2,515 

40.0  22.7  37.3 2,450 


Burdening  the  Furnace.  163 

Analyses  by  Gredt  show  clearly  that  the  substitution  of  MgO 
for  CaO  in  alumino-calcic  silicates  lowers  the  melting  point  until 
MgO  nearly  equals  CaO,  then  raises  it  sharply  as  CaO  is  com- 
pletely replaced  by  MgO,  thus: 

Melting  point, 

SiO2.  A12O3.  CaO.  MgO.                                           degrees  F. 

40.39  23.05  33.87                       2.69 2,510 

41.74  23.82  23.33  11. M 2,465    JgJ'  f 

42.20  24.09  39.66  14.05 2,465    p.  413. 

43.68  24.93  8.14  23.25 •. 2,520 

44.19  25.22  4.12  26.47 2,570 

44.72  25.52  0.0  29.76 2,725 

That  the  melting  points  of  slags  are  influenced  primarily  by 
their  degree  of  basicity  is  shown  by  the  following  analysis 
selected  at  random  from  Boudouard's  experiments : 

Melting  point, 
SiO2.  A12O3.          Total  acids.     Total  bases.  degrees  F. 

54.8  0  34.8  65.2 2,660 

26.6  31.4  38.0  62.0 2,625 

23.9  20.3  44.2  55.8 2,695 

35.2  10.0  45.2  54.8 2,625 

37.4  10.3  47.7  52.3 2,515 

38.6  16.4  55.0  45.0 2,500 

40.0  22.7  62.7  37.3 2,450 

Usually  slags  having  more  than  50  per  cent,  lime  will  fall  to 
powder  on  cooling,  owing  probably  to  a  change  of  volume  which 
they  undergo  as  the  result  of  a  molecular  rearrangement. 

Relation  of  Slag  and  Temperature. — The  degree  of  basicity 
of  the  slag  may  be  varied  by  varying  the  proportion  of  flux  used. 
By  this  means  two  properties  of  the  slag  are  changed,  both  of 
which  tend  to  increase  its  effectiveness ;  its  attraction  for  silica 
and  sulphur  is  increased  and  its  melting  point  is  raised.  The 
most  fusible  slags  have  the  acid  constituents  somewhat  in  excess 
of  the  basic,  and  therefore  any  increase  of  bases  tends  to  decrease 
fusibility.  On  the  other  hand,  a  large  excess  of  silica  tends  to 
make  an  infusible  slag,  but  the  infusibility  increases  more  rapidly 
by  addition  of  lime  than  by  increase  of  silica.  The  control  of  the 
hearth  temperature  and  consequently  the  grade  of  iron  is  largely 
dependent  upon  the  melting  point  of  the  slag.  It  is  not  easy  to 
get  the  hearth  temperature  very  far  above  that  point,  since  the 
excess  of  heat  is  absorbed  in  super-heating  the  slag  without 


164  Blast  Furnace. 

affecting  the  iron.  A  slag  with  a  low  melting  point  will  not  be  ac- 
companied by  hot  iron,  no  matter  how  great  an  excess  of  fuel  is 
used.  This  is  best  accounted  for  by  the  fact  that  the  layer  of  slag 
prevents  the  absorption  of  heat  by  the  iron.  As  a  result  the  tem- 
perature of  the  iron  is  largely  acquired  from  contact  with  the  .slag 
as  it  drips  through  it.  A  slag  which  melts  readily  is  not  long 
in  the  zone  of  combustion 'and  does  not  acquire  a  high  tempera- 
ture. A  refractory  slag,  on  the  other  hand,  passes  into  fusion 
slowly  and  becomes  super-heated  by  long  contact  with  the  heated 
gases  and  therefore  has  the  power  to  super-heat  the  iron  on  its 
passage  to  the  hearth.  This  serves  to  explain  the  well-known 
but  badly  expressed  fact  that  "  lime  gives  heat  to  a  furnace." 

Relation  of  Slag  and  Product — In  general  it  may  be  stated 
that,  other  things  being  equal,  a  high  hearth  temperature  will 
produce  a  high  silicon  and  low  sulphur  product,  and  a  basic  slag 
will  make  both  silicon  and  sulphur  low.  The  usual  explanation 
is  that  high  temperatures  facilitate  reduction  of  silicon  but  tend 
to  volatilize  sulphur,  while  the  basic  slag  holds  them  both  in 
check.  The  two  conditions  act  concurrently  in  restraining  the 
sulphur,  but  are  opposed  as  regards  the  silicon.  It  is  by  taking 
advantage  of  these  tendencies  that  the  control  of  silicon  and 
sulphur  is  effected.  Let  us  assume  by  way  of  illustration,  a  few 
examples : 

1.  High  temperature  and  basic  slag;  SiO2 -(- A12O3  below  45 
per  cent.    This  would  result  in  making  both  Si  and  S  low  in  the 
pig,  probably  less  than  i.oo  per  cent,  and  0.04  per  cent.,  respective- 
ly, hence  it  would  be  suitable  for  basic  steel  melting. 

2.  High  temperature  and  neutral  slag ;   SiO2  +  A12O3  about 
47  to  48  per  cent.    This  condition  would  result  in  increasing  both 
the  Si  and  S  in  the  pig,  the  former  much  more  than  the  latter, 
since  the  high  temperature  still  favors  reduction  of  Si,  and  it  is 
less  strongly  held  in  the  slag.     The  S  is  affected  by  the  change 
in  slag  also,  and  the  resulting  pig  might  run  1.5  per  cent.  Si  and 
0.05  per  cent.  S,  which  would  be  of  Bessemer  and  forge  grades. 

3.  High  temperature  and  acid  slag;  SiO2  +  A12O3,  exceeding 
50  per  cent.    This  would  probably  result  in  a  still  further  increase 
of  silicon  and  sulphur  for  the  same  reason  as  given  under  (2). 


Burdening  the  Furnace.  165 

The  pig  would  probably  analyse  2  to  3  per  cent.  Si,  S  under  0.06 
per  cent.,  and  would  be  of  foundry  quality. 

A  decrease  of  temperature  in  any  of  the  three  cases  under 
supposition  would  probably  result  in  a  lowering  of  Si  and  a 
rise  in  S.  It  is  not  possible  to  predict  fixed  results,  from  a  given 
slag  composition,  however,  as  results  are  affected  by  so  many 
conditions  as  to  be  always  uncertain.  These  figures  are  given 
simply  to  fix  the  ideas  by  a  concrete  example  of  what  might  be 
reasonably  expected.  It  has  been  shown  by  Howe  that  foundry 
and  forge  grades  of  iron  usually  accompany  slags  that  are  more 
basic,  and  white  and  charcoal  iron  accompanies  slags  that  are  Sw^"1 
less  basic  than  singulo-silicates,  in  which  the  ratio  of  oxygen  in 
the  bases  to  that  in  the  acids  is  I. 

Limit  of  Efficiency  of  Slags — The  limit  of  the  power  of 
slags  of  ordinary  degrees  of  basicity  to  hold  sulphur  is  probably 
not  much  above  2  per  cent,  of  sulphur.  As  we  have  seen,  the  sulphur 
present  in  the  charge  per  100  pounds  of  pig  is  usually  about  i 
pound.  In  order  that  the  sulphur  in  the  slag  may  not  exceed  2 
per  cent.,  therefore,  it  is  necessary  that  there  should  be  about  50 
pounds  of  slag  for  every  100  pounds  of  pig  made.  In  practice  it 
is  found  that  if  the  quantity  of  slag  per  ton  of  pig  falls  much 
below  TOGO  pounds,  the  extraction  of  sulphur  suffers  under  any 
conditions  of  temperature  or  slag  composition.  It  is  evident, 
therefore,  that  with  fuel  of  normal  ash  and  flux  of  usual  efficiency, 
the  ore  mixture  should  not  contain  less  than  an  average  of  8 
per  cent,  of  slag  forming  materials.  If  there  is  a  deficiency  of 
such  constituents,  it  can  be  supplied  by  adding  silica  in  some 
form  and  neutralizing  it  with  flux.  Silica  may  be  added  in  several 
ways.  The  preferable  source  is  a  lean,  siliceous  ore,  mixed  judi- 
ciously with  the  richer  ores.  A  very  good  substitute,  however,  is 
mill  cinder,  obtained  from  the  heating  furnaces  of  rolling  mills. 
The  cinder  from  a  steel  rolling  mill  is  tolerably  pure  ferrous 
silicate  low  in  phosphorus.  That  from  a  wrought  iron  rolling  mill 
will  be  higher  in  phosphorus.  The  cinder  from  a  puddle  mill, 
however,  should  not  be  used  unless  a  pretty  high  phosphorus 
pig  is  desired.  Sometimes  sand  or  siliceous  rock  is  used. 

It  was  formerly  the  custom  to  estimate  the  proportion  of 
bases  that  should  be  in  the  slag  for  given  results  on  the  basis  of 


166  Blast  Furnace. 

the  oxygen  ratio.  Identical  oxygen  ratios  may  give  slags  of  very 
•  iron  AKe,  different  ratios  of  acids  to  bases,  when  ALO3  is  reckoned  as 
acid.  It  is  found  in  practice  that  the  efficiency  of  slag  varies 
more  nearly  with  the  basicity  than  with  changes  in  the  oxygen 
ratio. 

Physical  Characteristics — To  the  practised  eye,  the  appear- 
ance of  the  slag  tells  much  concerning  its  composition  and  the  tem- 
perature of  formation.  A  slag  that  is  high  in  earthy  bases  has  a 
light  gray  to  bluish  granular  fracture  when  cold.  When  high 
in  lime,  slags  "  slake,"  or  crumble  to  powder  soon  after  cooling. 
This  tendency  is  retarded  by  the  presence  of  magnesia.  As  the 
proportion  of  bases  decreases,  the  slag  shows  a  vitreous  tendency 
— at  first  on  the  outer  edges  only,  but  as  the  acid  constituents 
increase,  it  may  become  glassy  throughout.  The  presence 
of  alumina  opposes  this  tendency,  and  gives  a  more  earthy 
appearance  than  silica  alone.  Siliceous  slags  can  be  drawn  out 
into  fine  strings  just  before  solidifying,  while  basic  slags  are 
very  short.  Hot  acid  slags,  when  run  into  the  granulating  pit, 
froth  up  into  light  fluffy  heaps,  while  basic  slags  sink  quietly  to 
the  bottom.  Other  things  being  equal,  the  slag  from  a  cold 
furnace  will  be  more  vitreous  than  from  a  hot  furnace.  This 
is  because  it  is  more  siliceous  since  less  silicon  has  been  reduced 
from  the  slag  and  gone  into  combination  with  the  iron. 

A  siliceous  slag  is  more  likely  to  carry  an  appreciable  quantity 
of  oxide  of  iron  than  a  basic  slag.  This  is  because  unsatisfied 
SiO2  will  seize  upon  any  unreduced  iron  that  reaches  the  fusion 
zone  more  readily  than  when  it  is  saturated  with  bases.  For 
this  reason  slags  from  a  cold  furnace  generally  have  a  dark  color 
and  high  specific  gravity,  particularly  when  improperly  prepared 
material  is  projected  into  the  hearth.  Calcareous  slags  some- 
times give  a  dark  color  when  a  furnace  is  in  trouble  without 
losing  their  earthy  appearance  or  containing  an  undue  proportion 
of  iron.  The  dark  color  appears  to  be  simply  a  stain,  probably 
caused  by  finely  divided  carbon. 

According  to  Vogt,  blast  furnace  slags,  when  allowed  to  cool 
slowly  tend  to  crystallize  into  definite  mineralogical  forms,  vary- 
ing with  their  compositions.  Bisilicate  slags  show  enstatite, 


Burdening  the  Furnace.  jgy 

augite,  and  wollastonite,  according  to  the  proportion  of  Ca  and 
Mg.  Singulo  silicates  show  olivine  and  melilite  and  other 
tetragonal  minerals,  according  to  the  ratio  of  CaO  to  the  oxides 
of  Fe,  Mn  and  Mg.  Pyroxene  appears  in  more  siliceous  slags. 
Feldspar  and  free  oxides,  such  as  quartz,  corundum  and  metallic 
oxides  are  never  found.  Sulphur  always  appears  as  a  monosul- 
phide  of  Ca,  Fe  or  Mn. 

CONTROL   OF    HEARTH    TEMPERATURE. 

For  the  production  of  different  classes  of  iron  the  silicon 
content  must  be  controlled  within  rather  narrow  limits.  For 
example,  less  than  i  per  cent,  of  silicon  is  usually  demanded  for 
basic  open-hearth  grade  of  pig,  but  such  an  iron  would  be 
entirely  unsuited  for  foundry  purposes.  On  the  other  hand, 
foundry  irons  usually  contain  upwards  of  3  per  cent,  of  silicon, 
but  such  an  analysis  would  be  prohibitive  for  basic  irons.  The 
chief  factor  in  the  control  of  silicon  is  hearth  temperature,  which 
in  turn  is  determined  largely  by  the  slag  composition.  With  a 
given  slag  composition,  however,  the  hearth  temperature  is 
capable  of  considerable  variation.  There  are  several  ways  in 
which  it  may  be  diminished  if  desirable.  The  most  immediate 
effect  may  be  obtained  by  using  a  proportion  of  cold  blast. 
Increasing  the  quantity  of  blast  would  give  the  same  effect,  and 
instead  of  checking  the  furnace  would  increase  its  output.  This 
is  equivalent  in  its  effect  to  adding  cold  blast,  since  the  increased 
quantity  of  air  passing  through  the  stoves  does  not  permit  each 
particle  to  be  heated  to  so  high  a  temperature.  The  effect  is  tem- 
porary, however,  and  the  furnace  soon  comes  to  equilibrium  on 
the  new  basis.  This  method  is  not  usual  now,  however,  as  it  is 
customary  to  blow  a  constant  quantity  of  air  per  minute  without 
variation.  If  the  rate  of  driving  cannot  be  increased,  the  cooling 
effect  may  be  obtained  by  increasing  the  burden,  which  is  equiva- 
lent to  a  diminished  fuel  consumption.  This  method  is  slower  in 
its  effect  since  no  result  is  apparent -till  the  new  burden  reaches 
the  hearth.  The  reverse  of  these  conditions,  namely,  decreased 
burden,  or  increased  blast  temperature,  will  result  in  increased 
hearth  temperature. 


168  Blast  Furnace. 

BURDENING  THE  FURNACE. 

The  problem  of  burdening-  a  furnace  properly  presents  two 
distinct  phases,  which  may  best  be  designated  by  the  titles  of 
theoretical  and  empirical.  The  theoretical  phase  presents  itself 
when  one  is  dealing  with  new  problems,  such  as  unfamiliar 
materials,  whether  ores,  fuel  or  fluxes,  or  when  using  familiar 
materials  in  unfamiliar  proportions,  such  as  in  filling  a  furnace, 
preparatory  to  blowing  in.  The  empirical  phase  is  present  when 
a  furnace  is  operating  with  fixed  sources  of  supply.  In  other 
words,  under  strange  conditions  materials  must  be  used  according 
to  analysis,  and  the  proper  proportion  determined  by  calculation, 
but  after  approximately  proper  conditions  with  fixed  materials 
are  once  attained,  the  diurnal  variations  may  best  be  watched 
and  corrected  by  simple  inspection,  checked  by  regular  analyses. 

THE  THEORETICAL   PHASE. 

Limitations  of  Slag  Control — In  order  to  obtain  a  slag  of 
an  approximately  given  composition  from  a  given  set  of  materials 
it  is  necessary  first  to  know  definitely  the  composition  of  the 
materials  themselves,  and  then  to  arrange  and  adapt  them  to 
produce  the  required  result.  Since  each  member  of  a  furnace 
burden  contains  gangue  elements  in  tolerably  fixed  proportions, 
it  is  not  always  possible  to  produce  results  that  are  too  closely 
limited.  For  instance,  it  would  be  manifestly  impossible  to 
produce  a  slag  having  an  alumina-silica  ratio  of  I  to  10  when 
the  ratio  in  the  raw  materials  is  i  to  4.  By  grouping  the  A12O3 
and  SiO2  together,  however,  as  the  acid  portion  of  the  slag,  and 
treating  them  as  a  unit,  the  difficulty  of  calculation  is  lessened 
without  in  any  wise  affecting  the  unalterable  conditions  of  the 
problem.  As  a  rule,  the  SiO2  and  A12O3  of  Lake  Superior  ores 
are  so  proportioned  that  an  average  ore  mixture  will  approximate 
the  ratio,  SiO2  to  A12O3  =  4  or  5.  Resulting  slags,  however, 
generally  show  a  ratio  of  about  2  to  3,  due  to  the  addition  of  Al 
from  fuel  and  stone,  and  subtraction  of  Si  by  the  pig  iron. 

Slag  Calculation. — For  the  purpose  of  illustrating  how  such 
diverse  materials  may  be  arranged  and  combined  to  give  definite 
results,  let  us  assume  the  following  composition  of  materials  in 
per  cent,  or  pounds  per  100  pounds: 


Burdening  the  Furnace.  169 

Material.              SiO2.  A12OS.  CaO.  MgO.  Mn.  P.  S.              Pe.         C. 

Fuel     f).30  3.00  1.00  0.70  .,.  0.020  0.75         86.5 

Ore    7.49  0.81  0.15  0.12  0.45  0.024  ...        55.75 

Flux    O.Gi  0.32  54.20  0.35  ...  0.004  

Let  us  assume  that  the  resulting  pig  will  contain  3.4  per  cent. 
C,  1.5  per  cent  Si  and  94  per  cent.  Fe,  and  that  the  slag  will  con- 
tain 47  per  cent.  SiCX  +  A12CX,  and  51.5  per  cent,  bases,  a  ratio 
of  acids  to  bases,  i  to  i.i. 

The  problem  is  simplified  by  dividing  it  into  three  steps,  as 
follows : 

1.  Find  the  available  base  and  slag- forming  constituents  of 
the  flux. 

2.  Find  the  flux  needed  and  weight  of  slag  formed  by  the 
fuel  and  its  available  carbon. 

3.  Find  the  flux  needed,  weights  of  slag  formed  and  fuel  con- 
sumed by  the  ore. 

With  these  figures  it  is  easy  to  find  the  total  flux  required,  and 
amount  of  slag  formed,  and  also  the  probable  phosphorus  content 
of  the  resulting  pig.  If  the  flux  requirement  for  each  ore  is  ex- 
pressed in  pounds  per  hundred  of  ore,  it  greatly  simplifies  the  task 
of  changing  the  burden  of  the  furnace  whenever  desired. 

Flux  Requirement — In  the  case  of  the  flux,  the  available 
base  in  the  stone  is  as  follows : 

Acids.  Bases. 

SiO2 0.64  CaO 54.20 

A1203 0.32  MgO 0.35 

0.96  54.55 

1.1  slag  ratio.  1.05  neutralized  by  acids. 

0.96  53.50  available  base. 

0.96 

1 .056  bases  needed. 
100.0 

—  =r  1.87  =  efficiency  of  flax. 

53.5 

The  non-volatile,  irreducible  parts  of  the  flux  which  make  up 
the  slag=forming  constituents  of  the  stone  are  SiO2  +  A12O3  + 
CaO  +  MgO,  and  they  equal  55.5  per  cent,  of  the  stone. 

Fuel  Requirements — In  the  case  of  the  fuel,  the  flux  needed, 
the  slag  formed  and  the  available  carbon  may  be  found  as  fol- 
lows: 


170  Blast  Furnace. 

Acids.  Bases. 

SiO2 5.30  CaO 1.00 

AI2O3 3.00  MgO 0.70 


8.30  1.70 

1.1  slag  ratio. 

8.30 

9.1 3  bases  needed. 
1.70  bases  present. 

7.43  bases  to  be  added. 
7.43  X  1.87  —  13.89  pounds  stone  needed  to  flux  ash. 

56 
0.75  X  —  X  1.87  =    2.45  pounds  stone  needed  to  flux  sulphur. 

32 
Total 16.34  pounds  stone  needed  per  1OO  pounds  fuel. 

The  slag  formed  by  the  ash  and  sulphur  of  the  fuel  equals  the 
ash  and  sulphur  plus  the  flux  needed,  thus : 

8.3  +  1.7  +  0.75  +  (16.34  X  0.555)  =  19.81  pounds,  weight  of  slag  per  1OO 

pounds. 

19.81  X  0.25  =  5.0  pounds  carbon  needed  to  inelt  slag. 
86.5  —  5.0  =  81.5  per  cent,  available  carbon. 

Ore    Requirements — In  the  case  of  the  ore;  the  flux  needed 
and  slag  formed  may  be  found  as  follows : 

Acids.  Bases. 

SiO3 7.49  CaO 0.15 

A12OS 0,81  MgO 0.12 

%  MnO 0.20 

3.30 
Less  1.80  reduced  to  Si.  0.47 

6.50  to  be  fluxed. 
1.1  "lag  ratio. 

6.50 
6.50 

7.15  bases  needed. 
0.47  bases  present. 


6.68  bases  to  be  added. 

6.68  X  1.87  —  12.49  pounds  stone  for  1OO  pounds  ore. 
94.00- 

—  =  1.686,  number  tons  ore  to  make  1  ton  pig. 
55.75 
1.086  X  0.1249  —  0.2106  tons  stone  per  ton  pis. 

The  slag  formed  by  the  ore  per  ton  of  pig  may  now  be  found 
by  simply  adding  the  slag  forming  constituents  of  the  ore  to  those 
of  the  stone  needed  to  flux  it,  thus : 

6.5  -f  0.47 

X  1.686    -  0.1175  tons  slag  from  the  ore. 

100 


Burdening  the  Furnace.  171 

55.5 

X  0.210G  —  0.1109  tons  slag  from  the  stone. 

100 

0.2344  total  slag  due  to  ore. 

Fuel  Consumption — Having  found  the  quantity  of  slag 
formed  by  the  ore  and  its  flux  per  ton  of  pig,  we  may  ascertain  the 
fuel  requirement  per  ton  of  pig  by  simply  adding  that  needed  by 
the  slag  to  that  needed  by  the  pig,  as  follows : 

0.2344 
For  the  formation  and  melting  of  the  slag,  —  — 0.059  parts  C. 

For  reduction,  impregnation  and  melting  pig  containing  1.5%   Si  =  0.685  parts  C. 

Total  carbon  required  for  pig  and  slag 0.744  parts  C. 

0.744 

X  2240  —  2<)45  pounds  coke  per  ton  of  pig. 

81.5 

Allowing  6  per  cent,  for  braize,  the  fuel  consumption  per  ton  of  pig  will  be 
about  2150  pounds. 

Total    Slag The  total  quantity  of  slag  per  ton  of  pig  will  be 

as  follows : 

Pounds. 

From  the  ore,  0.2344  X  2240  — 525.0 

From  the  fuel,   0.1981    X2045   = 405.1 

Total  slag  per  ton  of  pig  = 930.1 

Total    Stone — The  total  quantity  of  stone  per  ton  of  pig  is  as 

follows : 

For  the  ore,  0.2106  X  2240  = 471.7  pounds. 

For  the  fuel,  0.1634   X  2045  = 334.1  pounds. 

Total  stone  per  ton  of  pig  — 805.8  pounds,  which  is  21.4  per  cent. 

figured  on  the  burden  and  36  per  cent,  figured  on  the  product. 

Furnace  Charge — Based  on  a  5-gross  ton  charge  of  fuel,  the 
rounds  of  the  charge  would  be  composed  as  follows : 

Pounds. 

Fuel 11,200 

Ore    21,500 

Stone    .  4,500 


Phosphorus  Content  of   Pig — Assuming  that  practically  all 
the  phosphorus  in  the  charge  enters  the  j 
expected  there  may  be  found  as  follows : 


of  the  phosphorus  in  the  charge  enters  the  pig,  the  percentage  to  be 


Pounds  pei- 
ton  pig. 

From  the  ore,  0.024  X  1.686  X  22.4  = 0.9060 

From  the  fuel,  0.020   X   20.45  — 0.4090 

From  the  stone,  0.004  X  7.99  — 0.0320 

1.347 
1.347  X  100 

< =  0.06  per  cent.  P. 

2240 


S3 


.1 


«  "  S 


Is 
tf* 


U  a  JM    .34 

+  1  g  -3 


H    H  * 

Q  »*  3^ 

2  3  « 

Ofc  h« 


®*          •  TH 

-5  "  oT 

i!i  I 

IP  H 

35  s 


•no^  jad  uon 
^     I  -dmnsuoa     ian, 


s  s  §r 

'of   of    of 


of    oC    flf    fl(  • 


OO 
- 

on 


•Sid-sqtooiJad 


•Sid  -sqi  ooi  Jad 
OO    SB     uoqjt?o 


•Sid-sqiooiJad 
BOO    SB   uoq-iBO 


•Sid  -sqi  ooi  Jad 
auo^s  jo  8OO 
£q  uaio^s  uoqjBO 


•Sid  ui  snjoqd 
-soqd 


•Sid  uo^  jad 

3fDO^S   IB^O^    &C[ 

paidnooo    aoBdg 


oo      10 


»o     aq 
eo     »i 


S   8   5   8   fe   12 


oo 

cs'       Os" 

oi     w 


oo 

C5       c: 

el  •  9i 


oooo 


oo 

as       c: 

OT    9i 


oo 

cs'       a» 

9i    01 


' 


•Sid 

u<4  jad  janj  Aq 
paidnooo    ao^dg 


-Sid  uo^     |  jj 

jad    euo^s  Aq         • 

I  paidnooo    aoBdg  |  g 

~rs]d~]ll 

uo;  jad  ajo 
pafdnooo    a 

!     '8^03  uo^  jod       pL( 
<IH  8  pspaau  JH    W 


•9JIOQ 

uanq  o^  g^ntiim 
aad   papaau  '  oiy 


•Sid  -sqi  001 
jad  9>ioo  ^qSia^ 


•lanj 

ajo  tuojj 
•sqi     001 
jad  SB{g  jo  -^ 


pu« 
Sid 


•jan  j  pu«  aao 
joj  Sid  -sqt  ooi 
jad  papaau  auocjg 


•paxnp 


•Sid  -sqi 
OOT   aad   anSuBO 


•Sid  -sqi  OOT 
papaau    8o 


. 

^  -Sid  -sqi  001 
aoj  papaau    8JQ 


£    3 


8   8   S 


oo'     n 


of     m 


sf 


^    c» 

S    8 


e»    ei 


S    8    8    S    3' 


>q    « 


°' 


a  $;  a 


S     ' 


oooo 

3    3 


oooo 

S    3* 


oeo 


socc 

3    3 


55    53    g 


paup  aao  "I 


!£§  182 


S 
P,  S 


•gjr» 

1-1= 

^  ? 


o*a  ^ 


li  s!! 


>>w  2 

flSS: 

|8 

V.B     - 

ia  . 
^  >»••  - 


4»O 

ss 


all     -53I 


s! 

c  ° 

Ig 
feS 

•3^ 
•Sfr 


*i- « 

^    §53 
«| 

:.I^ 

=  |1x 

rtC«> 
J«Jj 

^^      ^ 
-   H--     ° 

I    O 


S    ^  I.81 


§!y g  § 

18S  I  .. 


M0   "c    °- 

2*1   §  § 

•S^fe    o    + 


16 

38.7  +  38. 


y  be  found  as  follows 
coke  (85$  of  99.2  Ibs.) 
by  stone  (/•) 
nated  in  pig  i 


i 


O2 


to 

I 

^a 
•is 


quals  3 

53%  ore 
in  t 
tol 
mp 


,  o 
-bon  i 
st 


tl 

^     "HI  a 
3    gifeg 
o    |llrs 

.     eo   .  o  o-  - 

«j§    4-  Jo*1' 

rfS    ._3g^ 

sM™" 

583  a8^ 

TKlrf   cOa-P- 


to  be  burned 
Ibs.  C  requir 
anied  by  3i)8.8 
C  +  93.59  O2  ( 
02.48  CO  +  C 
total  carbon 
41.17  Ibs 
.5  =  1  " 


w  g     2&3/SV9S'  J 

3£  l^llii^a 

IB  loSteN- 


TT      I  I 

as    a> 

is  fe 


,1 


a  s 


S 


+ 


£>  <M  (S 

o  S  J 

I  s$ 

«     57    -g  +  " 

^2      co       o3  ^  ^ 

o        I      /-s  °V  w 

a       I       w  co  | 

|  1 1  §  § 


-f 


174  Blast  Furnace. 

Other  Methods  of  Calculation — Methods  have  been  devised 

for  performing  slag  calculations  mechanically  by  means  of  mova- 

inst.  jour.,    ble  scales  and  by  means  of  the  slide  rule,  but  their  application  is 

P. '151!    limited  to  the  given  conditions  for  which  they  are  arranged,  and 

they  have  not  been  adopted  generally. 

r.  A.  i.  M.  E.,          Other  methods  of  numerical  calculation  exist  and  have  their 

advocates,  but  they  show  no  advantage  over  the  method  used  here. 

iron  Age,    Graphical  methods,  when  running  for  considerable  periods,  under 

Dec.  3, 1891, 

Feb.  3,1892,    fixed  conditions,  may  have  some  advantages,  however. 

Effect  of  Ore  Richness — Influence  of  ore  composition 
upon  the  consumption  of  fuel  and  flux  and  also  upon  the  quan- 
tity of  blast  required,  stove,  engine  and  boiler  capacities,  gas  vol- 
umes and  carbon  ratio  is  shown  by  the  preceding  table.  It  should 
be  observed  carefully  that  the  relations  are  based  upon  thorough- 
ly dehydrated  ores.  For  a  given  iron  content  in  the  natural  state 
the  results  will  be  lower  in  proportion  to  the  amount  of  moisture 
present : 

THE   EMPIRICAL   PHASE. 

The  foregoing  statements  constitute  the  gist  of  the  theoretical 
phase  of  burdening  a  furnace.  Such  calculations  are  exceedingly 
useful  in  investigating  the  results  which  might  reasonably  be 
expected  from  a  given  mixture  of  raw  materials,  and  the  facts 
will  probably  come  very  close  to  expectations  while  everything 
runs  smoothly.  It  is  much  safer,  however,  to  judge  the  needs  of 
a  furnace  by  what  comes  out  of  it  than  by  what  goes  in,  and  it  is 
at  this  stage  that  observation  and  practical  experience  are  of  the 
utmost  value.  This  phase  of  burdening  may  be  denominated  the 
empirical  phase. 

Watching  the  Furnace There  are  two  cardinal  points  in  the 

condition  of  a  furnace  which  must  be  carefully  watched,  viz.,  the 
temperature  of  the  hearth  and  the  proportion  of  flux.  If  these 
two  factors  are  right  the  furnace  must  work  well.  There  are 
many  causes  for  the  interruption  of  proper  temperature  condi- 
tions, chief  of  which  may  be  mentioned  too  heavy  burden,  leaking 
water  blocks,  improper  combustion,  improper  blast  quantity,  ir- 
regular movement  of  stock.  There  are  several  indications  by 
which  the  temperature  of  the  furnace  hearth  may  be  judged  with 


Burdening  the  Furnace.  175 

sufficient  accuracy  for  practical  purposes.  It  is  not  necessary  to 
estimate  the  hearth  temperature  according  to  any  absolute  scale 
of  degrees.  It  is  necessary  to  judge  only  by  comparison  whether 
the  temperature  is  above  or  below  the  point  desired  for  the  work  in 
hand.  The  skill  of  the  metallurgist  is  better  manifested  by  knowl- 
edge of  the  temperature  needed  for  certain  results  than  by  ability 
to  detect  fine  differences  in  temperature. 

Judging  Hearth  Temperature — The  most  direct  means  of 
judging  the  hearth  temperature  is  by  looking  directly  at  it  through 
the  peep  hole  in  the  tuyerestock.  If  the  hearth  is  cold  it  will  show 
a  reddish  or  lavender  light,  and  the  coke  can  be  readily  seen  as  it 
plays  in  the  blast.  If  the  hearth  is  very  hot  the  light  will  be 
dazzlingly  white,  so  that  the  coke  may  not  be  even  discernible. 
Intermediate  temperatures  will  present  intermediate  manifesta- 
tions. 

An  indirect  method  of  determining  the  temperature  of  the 
hearth  is  to  observe  the  temperature  of  substances  which  come 
out  of  it.  Chief  of  these  are  the  iron  and  the  slag.  The  tem- 
perature of  the  iron  may  be  judged  directly  by  its  appearance  or 
indirectly  by  its  silicon  and  sulphur  content.  The  iron  has  a 
high  initial  temperature  when  it  runs  from  the  furnace  with  a 
clear,  rapid  flow,  'free  from  scum  or  sparks,  and  does  not  readily 
skull  or  chill  in  the  bottom  of  the  runner.  Such  iron  is  likely 
to  be  fairly  high  in  silicon.  Cold  iron  usually  sparks  in  the  run- 
ner and  has  a  scum,  which  may  vary  from  thin,  milky  flakes, 
which  dot  the  surface  of  the  stream  when  slightly  cold,  to  glob- 
ules of  solid  iron,  known  as  buckshot,  when  very  cold  and  high 
in  sulphur.  Such  iron  usually  chills  in  the  runners  before  reach- 
ing the  last  pigs  in  the  bed,  and  is  apt  to  be  low  in  silicon.  On 
the  other  hand,  some  irons  rich  in  graphite,  though  made  in  hot 
hearths,  lack  fluidity,  and  irons  made  in  the  presence  of  very 
basic  slags  may  be  very  low  in  silicon  and  yet  possess  great  fluid- 
ity, owing  to  a  high  initial  temperature.  It  is  evident  therefore 
that  in  order  to  judge  hearth  temperature  by  the  iron  made  in 
it,  it  is  necessary  to  know  something  of  the  existing  conditions 
and  to  take  their  influence  into  account. 

The  hearth  temperature  may  be  judged  also  by  the  slag  pro- 
duced in  it.  The  absolute  temperature  of  the  slag  that  follows 


176  Jllnst  Fur  mice. 

the  iron  from  a  furnace  usually  appears  to  be  much  higher  than 
that  of  the  iron  which  precedes  it.  Since  the  layer  of  slag"  is 
nearer  the  tuyeres,  it  would  naturally  have  a  higher  temperature 
than  the  iron  below  it.  Moreover,  owing  to  the  difference  in 
their  respective  specific  heats,  the  slag  contains  nearly  50  per  cenL. 
more  heat  per  pound  than  the  iron  does,  and  radiates  it  much 
faster,  thereby  appearing  to  be  hotter.  The  relative  temperature 
of  slag  may  be  estimated  while  it  is  flowing,  from  its  color  and 
fluidity.  Under  ordinary  conditions  the  whiter  the  light  and 
greater  the  fluidity,  the  higher  the  temperature.  Hot  slag  usually 
gives  off  a  cloud  of  whitish  fumes,  which  rises  slowly  from  its 
surface  while  it  flows.  The  appearance  of  a  piece  of  slag  after 
it  has  become  cold  may  tell  something  about  the  temperature  in 
which  it  was  made.  Usually  a  hot  slag  will  show  a  grayish  white 
color  on  the  fractured  surface  after  cooling,  and  will  have  a  low 
specific  gravity.  A  slag  made  in  a  cold  furnace,  examined  under 
the  same  conditions,  will  usually  be  heavy  and  dark  in  color. 

Another  indirect  means  of  judging  the  furnace  temperature 
is  by  observing  the  appearance  of  the  flame  of  the  waste  gases 
as  they  burn  in  the  stoves  or  under  the  boilers.  The  gas  which 
comes  from  a  cold  furnace  burns  with  a  thin,  bluish  or  lavender 
flame,  which  has  a  clear,  lambent  appearance.  The  gas  from  a 
hot  furnace  has  a  strong,  yellow  flame,  which  is  opaque,  and  it  is 
usually  accompanied  by  a  whitish  fume  which  increases  in  density 
as  the  temperature  rises. 

Varying  Hearth  Temperature — When  the  temperature  indi- 
cations show  that  a  furnace  is  about  to  go  "  off  her  grade,"  that  is, 
getting  a  bit  too  cold,  there  are  several  ways  in  which  it  may  be 
righted.  Sometimes  a  slight  increase  in  blast  temperature,  -such 
as  would  result  from  putting  on  a  fresh  stove,  will  suffice.  A 
more  positive  effect  may  be  obtained  by  somewhat  reducing  the 
quantity  of  blast.  A  persistent  coldness  indicates  insufficient  fuel, 
and  consequently  the  burden  should  be  reduced.  If  conditions 
are  such  that  a  furnace  becomes  quite  cold,  it  may  be  necessary 
to  charge  a  blank  of  fuel. 

When  a  furnace  works  too  hot,  one  of  two  courses  may  be 
pursued  to  advantage.  If  the  quantity  of  blast  be  increased,  it 
will  melt  more  rapidly  and  make  a  larger  output,  thereby  reduc- 


Burdening  the  Furnace. 


177 


ing  labor  costs  per  ton  and  fixed  charges.  If  the  blowing  capacity 
of  the  engines  has  been  already  attained,  the  other  alternative  is 
to  increase  the  burden,  and  thereby  to  reduce  the  costs  of  fuel 
per  ton. 

Effects  of  Cold  Furnace — If  the  furnace  is  allowed  to  get 
cold  with  any  kind  of  slag,  the  reduction  of  silicon  may  decrease  to 
the  vanishing  point.  Whenever  the  silicon  falls  much  below 
I  per  cent,  of  the  pig  with  sulphur  above  0.05  per  cent.,  it  is  gen- 
erally insufficient  to  cause  the  separation  of  much  graphite,  and 
mottled  or  white  iron  results.  As  the  silicon  in  iron  decreases, 
the  sulphur  generally  increases.  The  change  in  sulphur  is  not 
necessarily  the  result  of  the  change  in  silicon  content,  but  may  be 
partly  attributed  to  it.  There  are  three  possible  explanations  of 
the  rise  of  sulphur,  and  it  is  probable  that  the  total  effect  is  the 
result  of  all  three.  In  the  first  place,  it  is  claimed  by  some  that 
silicon  has  a  distinct  excluding  effect  upon  sulphur  and  that  in 
consequence  a  high  silicon  iron  cannot  take  up  more  than  a  few 
tenths  per  cent,  sulphur.  In  the  next  place,  the  usual  explana- 
tion of  low  sulphur  in  iron  made  in  a  hot  hearth  is  that  the  intense 
heat  volatilizes  a  large  part  of  the  sulphur  and  conversely  a  cold 
furnace  will  allow  it  to  enter  the  pig. 

The  final  consideration,  which  is  by  no  means  a  minor  one,  is 
the  decrease  of  basicity  of  the  slag  when  the  expected  quantity 
of  silicon  is  not  reduced  from  the  siliceous  components  of  the 
charge.  A  very  simple  calculation  shows  that  if  a  furnace  is 
making  iron  with  1000  pounds  of  slag  per  ton  of  pig,  the  transfer 
of  i  per  cent,  of  silicon  from  the  iron  to  the  slag  in  the  form  of 
2.14  times  as  much  SiO2  will  change  the  percentage  of  acids  in 
the  slag  from  4Jl/2  to  50  per  cent.,  and  the  ratio  of  bases  to  acids 
from  i.i  to  i,  which  is  equivalent  to  a  decrease  of  over  10  per 
cent,  in  the  quantity  of  flux  used.  A  proportionate  change  in  the 
slag  composition  resulting  from  still  less  reduction  of  silicon, 
would  profoundly  affect  the  desulphurizing  power  of  the  slag. 

Under  improper  conditions  of  temperature  and  slag  composi- 
tion, insufficiently  digested  material  is  likely  to  descend  into  the 
furnace  hearth.  In  consequence  a  considerable  quantity  of  un- 
reduced oxide  of  iron  may  enter  the  slag  to  combine  with  the  un- 
reduced silica.  A  slag  which  is  highly  charged  with  ferrous  sili- 


Tr.  A.  I.  M  E., 
XXIII.,  p.  382. 


Thop.  Turner. 
"Metallurgy," 

p.  200. 


178  Blast  Furnace. 

cate  has  a  low  melting  point  and  great  fluidity,  and  exerts  a 
strongly  corrosive  effect  upon  the  lining  or  hearth  accretions.  It 
is  consequently  known  as  a  "  scouring  "  slag.  With  more  regular 
and  better  watched  conditions  such  a  slag  occurs  less  commonly 
now  than  formerly. 

Another  phenomenon  which  is  peculiar  to  cold  hearths  is  the 
occurrence  of  "  buckshot."  It  appears  in  the  form  of  unaggre- 
gated  globules  of  iron  which  are  intermingled  with  the  slag  that 
floats  on  the  top  of  the  flowing  iron,  or  which  are  entangled  me- 
chanically in  a  cold  and  viscous  slag.  The  globules  appear  to  be 
chiefly  iron  which  has  been  but  partly  carburized.  They  have 
undergone  fusion  and  yet  have  been  unable  to  coalesce  success- 
fully, owing  to  the  resistance  of  the  pasty  slag. 

Control  of  Manganese — Like  the  silicon  and  sulphur,  the 
manganese  which  enters  the  pig  varies  with  the  temperature  and 
slag  composition.  Since  a  high  temperature  favors  reduction  of 
manganese,  it  follows  that  the  hotter  the  furnace,  the  larger  will  be 
the  proportion  of  the  manganese  present  which  will  enter  the  pig. 
On  the  other  hand,  since  oxide  of  manganese  acts  as  a  base,  it  i-s 
interchangeable  with  lime  in  the  constitution  of  the  slag.  A 
highly  calcareous  slag,  therefore,  will  tend  to  release  more  man- 
ganese for  reduction  than  a  siliceous  slag.  Under  ordinary  con- 
ditions it  is  safe  to  count  on  the  reduction  to  metal  of  50  to  75 
per  cent,  of  the  total  manganese  present  in  the  charge,  and  the 
remainder  will  enter  the  slag.  Its  power  of  uniting  with  sulphur 
and  excluding  it  from  the  iron  makes  it  desirable  to  have  6.5  to 
0.75  per  cent.  Mn  in  the  pig,  which  indicates  that  there  should  be 
in  the  furnace  about  i  pound  Mn  for  every  100  pounds  of  pig 
made,  or  about  one-third  per  cent,  of  the  charge. 

Control  of  Phosphorus. — As  stated  before,  the  phosphorus 
content  of  pig  iron  is  practically  independent  of  furnace  manipu- 
lation but  depends  almost  entirely  upon  the  nature  of  the 
materials  used.  The  source  of  the  phosphorus  is  in  the  fuel  and 
flux  as  well  as  the  ore,  and  that  fact  must  be  reckoned  with  in 
making  the  furnace  charges.  Probably  never  less  than  90  per 
cent,  of  the  phosphorus  present  enters  the  iron  and  more  often  it 
is  nearer  100  per  cent.  It  is  safer,  therefore,  to  assume  that  it 
will  all  enter  the  iron,  particularly  when  a  rigid  phosphorus  limit 
is  required. 


Burdening  the  Furnace.  179 

Control  of  Carbon. — The  quantity  of  carbon  which  enters  pig 
iron  is  independent  of  the  composition  of  the  furnace  mixture 
and  is  not  directly  affected  to  any  great  extent  by  furnace  con- 
ditions. The  usual  range  of  carbons  in  pig  iron  is  from  3  to  4.25 
per  cent.,  but  the  great  majority  run  from  3.25  to  4.00  per  cent., 
and  this  quantity  is  tolerably  constant,  whether  the  iron  is  gray 
or  white.  The  color  of  the  iron  is  determined  by  the  proportion 
of  the  carbon  that  exists  as  graphite  and  not  by  the  total  quantity 
of  carbon  present.  The  total  quantity  of  carbon  present  in  pig 
iron  is  profoundly  affected  by  the  presence  of  other  elements  in 
the  pig.  Both  silicon  and  phosphorus  exert  a  strong  excluding 
tendency  upon  carbon,  so  that  practically  no  carbon  will  be  re- 
tained by  pig  iron  which  contains  15  to  20  per  cent,  of  either  of 
them.  On  the  other  hand,  manganese  has  a  strong  attraction  for 
carbon  and  manganiferous  irons  are  proportionately  higher  in 
this  element.  The  interrelations  may  be  expressed  approximately 
by  this  formula,  wherein  the  quantity  of  each  element  is  expressed 
in  per  cent. : 

Total   carbon  =  4.5  —  0.25  Si  —  0.3  P  -f-  0.03  Mn. 

The  variations  of  the  different  elements  in  gray  and  white 
irons  may  be  represented  graphically  as  follows : 

Titanium. — The  presence  of  titanium  in  ores  of  iron  had  the    E.  M.  j., 
reputation  of  causing  infusible  and  troublesome  slags,  due  to  the   p-  ssb-' 
presence  of  titanate  of  lime  and  other  titaniferous  compounds. 
That  this  reputation  of  titanium  is  unjustifiable  is  the  claim  of 
A.  J.  Rossi.     He  states  that  titanates  are  ^iot  infusible,  but  that  _ 

Tr.  A.  I.  INT.  j 

in  slags  having  about  60  per  cent,  of  acid  constituents,  as  much   xxl->  p-  83-- 
as  35  per  cent.  TiO2  was  substituted  for  SiO2  without  decreasing 
the  fusibility  of  the  slag.     More  recent  experience  has  justified   }™2(feis96 
his  claim.  P- 464-  ' 

TiO2  is  not  readily  reduced  by  the  influences  in    the    blast    M 
furnace,  and  therefore  titanium  is  rarely  found  in  pig  iron. 

Desirab!e  Ores — There  are  several  points  beside  its  composi- 
tion which  deserve  consideration  in  deciding  the  desirability  of 
an  ore.  In  the  first  place,  it  should  have  enough  slag-making 
material  so  that  the  sulphur  may  not  exceed  2  per  cent,  in  the 
slag.  The  quantity  of  gangue  for  average  ores  should  not  be 


380  Blast  Furnace. 

less  than  8  per  cent.  Secondly,  it  is  desirable  that  the  ores  should 
lose  their  oxygen  as  high  in  the  furnace  as  possible,  so  that  little 
CO2  will  be  generated  below  the  point  where  it  can  attack  carbon. 
Thirdly,  a  moderate  carbon  deposition  is  desirable  to  disintegrate 
the  ore  and  facilitate  reduction.  An  excessive  deposit  is  to  be 
avoided  as  it  causes  packing  which  results  in  excessive  engine 
pressure  and  top  explosions. 

Condition  of  Pig — Pig  irons  which  are  to  be  used  for  the 
manufacture  of  other  metallurgical  products,  such  as  wrought 
iron  or  steel,  by  one  of  the  processes  of  conversion,  are  always 
classed  strictly  on  the  basis  of  composition.  If  analysis  shows 
that  the  various  elements  fall  within  the  required  limits,  the 
physical  appearance  is  usually  considered  quite  secondary.  With 
irons  that  are  to  be  used  without  change  of  nature,  however,  as 
in  castings,  the  physical  appearance  of  the  fractured  surface  is 
considered  an  important  indication  of  the  degree  of  suitability.- 
The  physical  appearance  follows  closely  the  composition.  Other 
things  being  equal,  the  higher  the  silicon — up  to  3  per  cent,  at 
least — the  darker  and  coarser  grained  the  iron.  As  silicon 
decreases,  the  fracture  is  lighter  and  closer  until  white  is  reached. 
Other  conditions,  however,  may  modify  the  effect  of  silicon.  An 
iron  made  with  a  hot,  limey  cinder  will  present  a  grain  whose 
openness  is  out  of  proportion  to  its  silicon  content,  while  high 
sulphur  tends  to  make  the  grain  close.  The  rate  of  cooling  also 
modifies  the  appearance ;  the  slower  the  rate,  the  larger  the  grain. 
It  is  for  this  reason  that  sand  pig  beds  have  been  generally  pre- 
ferred to  chills  for  foundry  irons.  The  advantage  is  somewhat 
imaginary,  however,  as  iron  of  the  same  composition  wrhich  has 
been  through  the  casting  machine  will  make,  when  remelted, 
quite  as  good  castings  as  the  sand  pigs.  The  following  analysis 
of  experiments  by  the  Bethlehem  Steel  Company  illustrates  the 
effect  of  chills  on  iron : 

Sand  pig. 

Si     3.000 

Mn     0.950 

P 0.770 

S 0.041 

G.    C 3.210 

C.    C 0.250 

T.    C 3.460 

T.    S 15,000  pounds.  41,000  pounds.  16,300  pounds.  17,000  pounds. 


Sand  pig 

Chill  pig 

Chill  pig. 

remelted. 

remelted. 

2.990 

2.910 

2.950 

0.950 

0.850 

0.840 

0.773 

0.769 

0.764 

0.041 

0.064 

0.071 

2.460 

3.022 

3.100 

0.920 

0.368 

0.257 

3.380 

3.390 

3.357 

Burdening  the  Furnace.  181 

From  the  first  two  columns  it  is  apparent  that  strength  is 
not  dependent  upon  silicon  alone,  but  follows  closely  the  condition 
of  the  carbon,  no  matter  how  that  condition  is  produced.  By 
comparing  the  results  with  the  originals,  it  is  evident  that  there  is 
little  or  no  change  during  remelting.  Less  "  kish "  is  formed 
on  chill  pigs  than  on  sand  pigs.  The  higher  percentage  of  com- 
bined carbon  permits  more  ready  remelting,  hence  less  time  for 
oxidation.  Beir/g  more  free  from  sand,  less  slag  is  formed  in 
remelting,  less  fuel  and  flux  are  needed  in  the  cupola,  and  cleaner 
castings  result.  The  advantage  of  clean,  uniform  pigs  for  steel 
melting  is  unquestioned. 

Composition  and  Appearance — The  external  appearance  of 
the  solidified  pigs  serves  to  some  extent  as  an  indication  of  com- 
position. Irons  high  in  silicon  generally  give  a  full,  rounded 
appearance  to  the  top  of  the  pigs.  Conversely,  irons  low  in 
silicon  generally  show  hollowed  tops  and  sharp,  aggressive  edges. 
A  wrinkled,  worm-eaten  appearance  to  the  top  of  the  pigs  gen- 
erally accompanies  a  high  sulphur  content. 


CHAPTER  V. 
ACTION  WITHIN  THE  FURNACE. 

Introductory. — The  factors  which  compose  the  materials  used 
in  the  blast  furnace  are  four,  namely,  fuel,  ore,  flux  and  air.  We 
have  seen  that  of  these  four  the  first  three  are  charged  at  the 
top  of  the  furnace,  while  the  last  is  forced  in  near  the  bottom. 
In  consequence,  we  have  in  the  furnace  what  may  be  described 
as  two  currents,  traveling  in  opposite  directions ;  a  slow  current 
of  solids  descending  and  a  rapid  current  of  gases  ascending.  The 
ascending  current  goes  about  as  far  in  a  second  as  the  descending 
current  goes  in  an  hour.  Although  the  former  is  gaseous,  its 
weight  per  ton  of  product  is  about  double  that  of  the  solid 
materials. 

THE    DESCENDING    CURRENT    OF   SOLIDS. 

When  the  bell  is  lowered  and  the  charge  slides  into  the 
furnace,  we  have  a  relatively  cold,  and  often  wet,  body  entering 
a  heated  atmosphere.  The  temperature  at  the  top  of  the  furnace 
is  usually  400  to  600  degrees  F.,  and  heat  is  rapidly  absorbed 
as  the  material  passes  downward.  According  to  Sir  Lowthian 
Bell,  the  temperature  of  the  stock  in  an  80  foot  furnace  has 
risen  to  1000  degrees  F.,  when  the  stock  has  reached  a  depth  of 
10  to  12  feet,  1500  degrees  F.,  at  20  feet,  and  1800  degrees  F. 
at  30  feet.  According  to  Le  Chatelier  the  temperature  before  the 
tuyeres  exceeds  3500  degrees  F.,  when  all  portions  of  the  charge 
present  exist  in  a  state  of  complete  fusion. 

Fuel. — The  effect  of  the  heated  gases  upon  each  of  the  three 
kinds  of  substances  in  the  charge  as  they  journey  through  the 
furnace  is  very  different.  The  fuel  is  least  affected.  It  absorbs 
heat  and  a  small  percentage  is  dissolved  by  CO2,  but  it  suffers 
otherwise  very  little  change  until  it  arrives  before  the  tuyeres. 
There  it  comes  in  contact  with  the  blast,  and  its  carbon  is  rapidly 
consumed,  forming  CCX  which  is  immediately  reduced  to  CO. 
This  gas,  mixed  with  the  residual  nitrogen  of  the  blast,  forms  the 

182 


Action  Within  the  Furnace.  183 

bulk  of  the  upward  current.    The  ash  of  the  fuel  continues  down- 
ward and  enters  the  slag. 

Flux — The  change  in  the  flux  is  of  a  very  different  nature 
from  that  of  the  fuel,  and  begins  much  sooner.  It  should  be 
recalled  that  the  flux  is  a  calcic  or  magneso-calcic  carbonate, 
having  the  formula,  CaCO3,  or  Ca(Mg)  CO3.  When  the  stone 
has  attained  a  temperature  of  about  noo  degrees  F.,  it  begins  to 
decompose  and  loses  some  of  its  CO2,  which  joins  the  upward 
gaseous  current,  leaving  as  a  residue  a  corresponding  quantity  of 
burned  lime,  CaO.  Thus  : 

CaCO3  =  CaO  +  CO2. 

As  the  temperature  of  the  stone  increases,  the  decomposition 
is  more  rapid,  and  it  is  probable  that  by  the  time  it  has  reached 
the  bosh  of  the  furnace,  practically  all  of  the  CO2  has  been 
expelled  and  only  the  CaO  remains. 

CaCO3  begins  to  decompose  whenever  its  vapor  pressure 
equals  that  of  the  superimposed  atmosphere.  Under  reduced 
pressure,  it  will  begin  to  decompose  at  about  1000  degrees  F. 
In  the  ordinary  atmosphere,  however,  the  decomposition  cannot 
become  complete  until  the  vapor  pressure  equals  the  atmospheric 
pressure,  which  requires  a  temperature  of  1493  degrees  F.  As 
the  pressure  in  the  bosh  of  a  modern  furnace  usually  approximates 
ij^>  atmospheres,  the  final  decomposition  there  of  CaCO3  cannot 
occur  at  temperatures  much  below  1600  degrees  F. 

CaO  is  infusible  even  at  the  highest  temperature  of  the  blast 
furnace  hearth.  However,  by  the  time  it  has  reached  the  hearth, 
it  unites  with  the  siliceous  and  aluminous  gangue  of  the  ore  and 
ash  of  the  fuel,  and  forms  a  fusible  silicate  or  slag,  commonly 
called  "  cinder,"  which  drips  down  and  accumulates  in  the 
crucible. 

Ore. — The  changes  in  the  ore  take  place  for  the  most  part 
in  the  top  of  the  furnace.  It  is  usually  the  first  member  of 
the  charge  to  be  attacked.  Unlike  the  stone,  its  first  change  is 
not  due  to  heat  alone,  but  to  the  reducing  power  of  the  gases, 
and  is,  therefore,  chemical  in  its  nature.  The  deoxidation  begins 
at  temperatures  differing  with  the  character  of  the  ores.  Easily 
reduced  ores  are  affected  at  400  degrees  F.,  arid  the  action 


184  Blast  Furnace. 

becomes  more  rapid  as  the  temperature  rises.  The  change  is 
usually  about  completed  by  the  time  the  temperature  of  1000 
degrees  F.  is  reached,  which  corresponds  to  a  depth  of  less  than 
20  feet.  Through  the  loss  of  its  oxygen,  the  ore  is  changed  to  a 
finely  divided  sponge  of  metallic  particles,  which  undergoes  little 
change  until  it  reaches  the  zone  of  fusion,  where  it  is  melted. 

THE   ASCENDING    CURRENT   OF   GASES. 

The  air  for  combustion  enters  the  furnace  through  the 
tuyeres  in  the  form  of  a  blast  under  pressure  ranging  in  different 
furnaces  usually  from  5  to  20  pounds  per  square  inch,  and 
occasionally  higher.  It  is  sometimes  used  at  atmospheric  tem- 
peratures, when  it  is  known  as  "  cold  blast,"  but  generally  it 
has  a  temperature  between  800  degrees  F.  and  1400  degrees  F, 
when  it  is  known  as  "  hot  blast."  The  blast  comes  immediately 
into  contact  with  the  highly  heated  coke,  the  carbon  of  which 
unites  with  the  oxygen  of  the  blast,  forming  CO2.  Any  moisture 
which  may  be  present  in  the  blast  is  broken  up  in  the  presence 
of  carbon  at  this  high  temperature,  forming  CO  and  free 

hydrogen,  thus: 

C  +  H2O  =  CO  +  H2 

The  CO2  formed  by  the  combustion  of  the  coke  comes  into 
immediate  contact  with  incandescent  particles  of  carbon,  and  is 
at  once  resolved  into  CO  by  the  "  carbon  transfer,"  thus : 
CO2  +  C  =  2CO. 

The  following  analyses  by  Van  Vloten  illustrate  these  inter- 
changes : 

O.  CO2  CO.  H.                   N. 

Middle  of  tuyere 13.0  6.0              0.0  0.75  80.50 

l893Si>C92s'     Edge  of  tuyere 0.0  13.5               6.0  0.25  80.25 

Between    tuyeres 0.0  0.0  33.75  1.75  64.50 

From  these  analyses  it  appears  that  directly  in  front  of  a 
tuyere,  free  oxygen  may  still  be  found,  and  that  it  is  associated 
with  CO2,  but  not  with  CO.  At  the  edge  of  the  tuyere  the 
oxygen  has  all  been  consumed  to  CO2  and  some  of  the  CO2  has 
been  already  reduced  by  fresh  carbon  to  the  condition  of  CO. 
Between  tuyeres,  neither  free  oxygen  nor  CO2  is  found,  but  all  of 
the  carbon  exists  in  the  form  of  CO.  As  a  result,  the  gaseous 


Action  Within  the  Furnace.  185 

current  starts  upon  its  upward  journey  with  the  following  approxi- 
mate composition  by  volume  : 

CO   ...........................................................  35  per  cent. 

II   and    Hydrocarbons  ...........................................    1  per  cent. 

N  ............................................................  64  per  cent. 

CO  is  an  unsaturated  compound  with  a  strong  tendency  to 
take  up  oxygen,  thereby  forming  CO2,  thus  : 
CO  +  O  =  CO2. 

This  action  is  strong  enough  to  attract  oxygen  from  combina- 
tion with  iron  at  elevated  temperatures,  although  it  is  largely 
neutralized  by  the  presence  of  any  considerable  proportion  of 
the  resulting  CO2. 

Action  of  CO  --  The  action  of  CO  upon  oxides  of  iron  is 
characterized  by  two  decidedly  marked  phenomena,  namely,  the 
removal  of  oxygen  and  the  deposition  of  carbon.  These  two 
reactions  usually  proceed  simultaneously,  but  from  the  nature  of 
the  changes  it  is  evident  that  the  reduction  must  occur  first.  The 
action  of  CO  on  ferric  oxide  may  be  represented  thus: 
3CO  +  Fe203  =  Fe2  f  3CO2. 

In  practice,  however,  this  reaction  is  never  complete,  and  a 
considerable  excess  of  CO  is  necessary  to  make  it  even  approxi- 
mately complete,  as  the  presence  of  the  resulting  CO2  tends  to 
undo  the  work  of  the  CO.  The  reduced  metallic  iron  is  left  in 
the  form  of  a  finely  divided  sponge,  which  is  keenly  susceptible 
to  reoxidation.  At  elevated  temperatures  the_  CO2»  formed  by  the 
above  reaction,  is  capable  of  again  giving  up  a  part  of  its 
oxygen  to  the  spongy  iron  in  accordance  with  the  following 
reaction  : 


which  acts  more  vigorously  as  the  temperature  rises.  It  is 
probable  that  at  all  temperatures  above  760  degrees  F.  the 
reduction  of  ore  by  CO  and  the  oxidation  of  the  resulting  sponge 
by  CO2  can  take  place,  and  but  for  the  law  of  "  Mass  action," 
a  deadlock  would  exist  in  all  but  the  very  bottom  of  the  furnace. 
The  great  excess  of  CO  as  compared  with  CO2  in  all  parts  of 
the  furnace  enables  it  to  maintain  activity,  even  at  high  tempera- 
tures, through  its  greater  concentration. 

The  second  phenomenon  of  the   action  of  CO  upon  ores, 


186  Blast  Furnace. 

namely  the  deposition  of  carbon,  is  due  to  the  power  of  the 
metallic  sponge  and  the  lower  oxides  of  iron  to  split  up  CO  in 
accordance  with  the  following  reaction : 

2CO  =  CO2  +  C, 

by  which  the  separated  carbon  is  deposited  as  a  fine  dust  on  the 
metallic  sponge.  In  this  reaction  the  iron  appears  to  act  only 
as  a  "  catalyser,"  since  it  does  not  enter  into  the  reaction,  but 
only  facilitates  it.  The  quantity  of  carbon  so  deposited  m?y 
amount  to  several  times  the  volume  of  the  ore.  As  it  is  deposited 
in  all  the  crevices  and  spaces  of  the  ore,  it  exerts  a  very  powerful 
disintegrating  effect  upon  it.  It  may  serve  also  to  remove  from 
the  ore  the  last  traces  of  oxygen  left  by  the  incomplete  action  of 
the  CO. 

From  experiments  in  the  laboratory  of  Sir  Lowthian  Bell 
at  Clarence,  England,  it  is  evident  that  the  activity  of  CO  is 
affected  not  only  by  its  purity,  but  also  by  the  rate  and  pressure 
of  the  gas  current,  as  shown  by  the  following  table : 


Iron  Agf, 
Feb.  11,  1897. 

Kind  of  ore. 
Precipitated    Ff>2O3 

,—Oxygen  < 
Slow 
current. 
40  30 

?xtracted.-> 
Fast 
current. 
80.60 
18.20 
50.70 
42.00 

^Carbon  deposited.- 
Slow            Fast 
current,     currenl 
79.70            335.40 
3.80                4.90 
12.60              22.30 
2.30                 3.90 

Elba   ore  

1  6  90 

Cleveland    ore  

37  30 

It  ousted  spathic  ore.. 

..13.00 

It  is  not  likely  that  the  velocity  of  the  current  increases  the 
activity  of  the  gas.  The  effect  is  attributable  rather  to  the  prompt 
removal  of  the  neutralizing-  presence  of  the  CO2  formed  by  the 
two  reactions.  Pressure,  however,  assists  materially  in  the 

TxviiT;  JMi'    action  as  it:  brings  the  substances  involved  into  firmer  and  more 
intimate  contact. 

It  was  shown  by  Laudig  that  the  rates  of  reduction  and 
carbon  deposition  are  not  dependent  upon  the  state  of  division  of 
the  ore,  but  appear  to  be  profoundly  affected  by  the  mineralogical 

TxxW;  pr'269.'   classification.     He  found  the  degree  of  susceptibility  of  the  usual 
ores  to  be  in  the  following  order : 

Carbon  deposited 

per  cent.  Carbon  deposited 

of  original  ore.  per  unit  of  iron. 

Mesaba  ores 23.61  0.3401 

Brown  hematites 12.94  0.2400 

Red   hematites 13.82  0.2296 

Blue  hematites 3.08  0.0501 

Magnetites 0.10  0.0017 


Action  Within  the  Furnace.  187 

Action  of  H. — Free  hydrogen  also  is  a  strong  reducing  agent. 
When  passed  over  heated  oxide  of  iron,  it  deoxidizes  it  even 
more  readily  than  CO,  in  accordance  with  the  reaction : 
FesO,  +  3H2  =  Fe,  +  3H2O. 

However,  the  fact  that  hydrogen  occurs  in  gases  escaping 
from  the  furnace  seems  to  indicate  that  it  does  not  perform 
reduction  in  the  furnace.  But  while  it  may  not  reduce  ore 
directly,  it. may  assist  in  the  reduction  by  diluting  the  CO2  or 
even  by  decomposing  it,  producing  CO  thereby,  thus  : 

H2  +  CO,  =  H2O  +  CO, 

which  tends  indirectly  to  faciliate  reduction.  The  presence  of 
hydrogen  has  another  beneficial  effect,  in  that  it  facilitates  the 
decomposition  of  the  limestone,  as  shown  by  the  following 
experiments  by  Bell : 

Time,  CO2       CO2  unde-    CO2  de-        H2O 

Temperature.  Atmos.     minutes,  removed,  composed,  composed,  formed. 

Bright  red Air  40  13.5  13.5  0  0 

Bright   red CO2  30  10.7  ...  0  0 

Bright  red H2  30  40.5  21.4  19.1  7.44 

The  presence  of  hydrogen  is  due  chiefly  to  the  decomposition 
at  the  tuyeres  of  the  moisture  from  the  blast  or  other  sources, 
thereby  forming  water  gas,  in  accordance  with  the  following 
reaction : 

H20  +  C  =  H2  +  CO. 

The  quantity  present  in  the  blast  varies  at  different  seasons 
of  the  year  and  different  conditions  of  the  weather.  It  usually 
ranges  from  y2  to  il/2  per  cent,  of  the  gases  by  volume,  the 
average  for  the  year  being  about  that  yielded  by  3.7  grains  H2O, 
per  cubic  foot  of  air,  which  amounts  to  0.9  per  cent,  of  the  gases 
at  the  hearth  and  0.8  per  cent,  at  the  downtake. 

Action  of  N. — The  nitrogen  of  the  gases  is  practically  inac- 
tive except  for  a  slight  tendency  to  unite  with  the  hot  carbon  to 
form  cyanogen,  thus : 

C  +  N  =  CN, 
and  to  unite  with  hydrogen  to  form  ammonia,  thus : 

N  +  H,  =  NH,. 

Both  cyanogen  and  ammonia  act  as  deoxidizers, .  and  therefore 
the  gases  start  on  their  upward  journey  as  a  powerfully  reducing 
organization. 


188  Blast  Furnace. 

INTERACTION    OF   THE    CURRENTS. 

The  objects  which  the  gases  encounter  as  they  rise  from 
the  hearth  are  the  incandescent  coke,  interspersed  with  drops  of 
molten  iron  and  slag.  The  melting  zone  of  the  furnace  has  its 
origin  at  the  tuyeres,  where  the  heat  of  combustion  is  liberated, 
and  extends  upward  to  a  greater  or  less  height,  according  to 
conditions.  Usually,  in  a  normally  working  furnace,  it  extends 
well  up  into  the  boshes.  The  top  of  the  zone  is  marked  by  the 
melting  of  the  reduced  iron  sponge.  The  molten  iron  then 
trickles  down  through  the  bed  of  incandescent  coke,  dissolving 
carbon  as  it  goes,  and  passing  through  the  layer  of  accumulated 
slag  into  the  crucible.  The  melting  point  of  the  carburized  iron 
rarely  exceeds  2200  degrees  F.,  but  the  fusion  of  the  partly 
carburized  sponge  probably  requires  a  temperature  higher  by 
several  hundred  degrees.  A  short  distance  below  the  fusing  zone 
of  the  iron,  the  siliceous  residue  of  the  ore  and  part  of  the  lime 
from  the  calcined  limestone  unite,  become  fluid  and  flow  to  the 
hearth.  Slags,  when  once  formed,  can  usually  be  remelted  at 
temperatures  of  2600  or  2700  degrees  F.,  but  owing  to  the  lumpy 
condition  and  lack  of  intimate  mixture  of  the  ingredients,  the 
temperature  of  slag  formation  is  usually  several  hundred  degrees 
higher.  The  ash  of  the  fuel  reaches  the  tuyere  unchanged  on 
account  of  its  protecting  coat  of  carbon,  but  as  soon  as  the  carbon 
is  burned  away  the  ash  unites  with  the  balance  of  the  lime  and 
joins  the  rapidly  accumulating  cinder. 

Toward  each  of  these  substances,  the  gases  in  the  hearth  are 
neutral.  The  first  change  which  comes  to  the  gaseous  current 
in  its  upward  journey  is  «the  addition  of  CO2»  liberated  by  the 
decomposing  limestone.  This  usually  amounts  theoretically  to 
about  3  per  cent,  of  the  gases  by  volume,  but  is  rapidly  changed 
to  CO  in  the  presence  of  the  hot  coke,  and,  therefore,  analysis 
rarely  shows  over  \y2  per  cent,  in  the  zone  of  decomposition. 
Hence,  by  the  time  the  gases  have  risen  to  a  point  20  feet  from 
the  top,  they  show  relatively  little  change  in  composition.  From 
that  point  upward  the  greater  part  of  the  reduction  of  ore  and 
the  deposition  of  carbon  takes  place  and  the  CO  of  the  gases  is 
rapidly  converted  into  CO2. 

Since  the  carbon  transfer  cannot  take  place  below  760  degrees 


Action  Within  the  Furnace.  189 

F.,  it  follows  that  it  is  very  desirable  to  keep  the  main  evolution 
of  CO2  in  the  extreme  top  of  the  furnace,  if  possible.  This  fact 
puts  a  premium  on  easily  reduced  ores  which  give  up  the  bulk 
of  their  oxygen  at  temperatures  below  that  of  the  carbon  transfer. 
Dense  ores,  which  resist  the  action  of  the  gases  until  they  have 
descended  to  hotter  parts  of  the  furnace,  always  require  a  higher 
fuel  consumption  to  compensate  for  the  large  loss  of  carbon  due 
to  the  action,  in  the  hotter  parts  of  the  furnace,  of  the  CO2  which 
has  been  evolved  by  the  reduction. 

We  have,  then,  three  sources  of  CO2  in  the  furnace :  ( I )  de- 
composition of  limestone,  CaCO3  =  CaO  +  CO2 ;  (2)  reduction 
of  ore,  Fe.,O3  +  3CO  =  Fe0  +  3CO., ;  (3)  deposition  of  carbon, 
2CO  =  C  +  CO2. 

The  first  case  differs  from  the  other  two  in  that  the  CO2 
evolved  by  the  stone  is  an  addition  to  the  gas  current  and  more- 
over is  not  a  stable  addition,  since  it  occurs  so  low  in  the  furnace 
that  it  is  practically  all  changed  to  CO  by  the  carbon  transfer. 
In  the  other  two  cases  the  CO2  is  the  result  of  chemical  changes 
within  the  gases,  and  the  changes  are  permanent. 

This  constantly  increasing  proportion  of  CO2  tends  to 
neutralize  the  reducing  powers  of  the  CO  in  two  ways :  by 
dilution,  and  by  its  tendency  to  give  up  part  of  its  oxygen  to 
the  freshly  reduced  spongy  iron.  This  latter  tendency  decreases 
with  lowering  temperature,  and  practically  ceases  at  760  degrees 
F.  We  can  safely  assume,  therefore,  that  in  the  extreme  top 
of  the  furnace  only  reducing  conditions  can  .exist. 

Composition  of  Gases  at  Various  Depths The  change  in 

composition  of  gases  at  various  levels  of  the  -  furnace  is  an 
indication  of  the  reactions  which  take  place  at  those  levels : 

Percentage  by  •          Percentage  by 

volume.  volume. 

Depth,  CO.  CO..  Depth.  CO.  COa. 

feet.  feet.  feot.  feet.  feet.  feet. 

Top     29.5  11.0  161/2 34.1  2.2    ISM, 

4 29.5  10.5  20 .' 35.1  0.7    p>  87< 

8 27.0  8.0  39 35.0  1.1 

10 32.0  7.0  52 35.2  1.5 

12 33.0  7.0  65.. 35.9  0.5    !»•«»» 

14 31.0  6.5  701/2 36.6  0.0 

Tuyeres , 37.7  0,8 


190  Blast  Furnace. 

From  inspection  of  the  column  of  CCX,  the  following-  cor- 
roborative conclusions  may  fairly  be  drawn :  that  CCX  is  formed 
at  the  tuyeres,  but  that  it  is  immediately  changed  to  CO  by  the 
presence  of  incandescent  coke ;  that  some  undecomposed  lime- 
stone reaches  a  depth  of  65  feet,  and  CO2  from  that  source  is 
evolved  from  that  point  to  a  point  about  20  feet  from  the  top ; 
that  the  carbon  transfer  (CO2  +  C  =.  2CO)  takes  place  at  all 
points  between  the  same  levels ;  and  that  above  20  feet  the 
reduction  of  ore  takes  place  with  a  consequent  rapid  increase 
of  CO2. 

Action  of  CO2. — The  oxidizing  power  of  CO2  is  manifest  at 
all  temperatures  above  700  degrees.  At  710  degrees,  according  to 
Ackerman,  it  attacks  carbon,  and  at  760  -degrees,  Bell  found  that 
it  oxidized  the  iron  sponge.  The  latter  reaction  is  partially  off- 
set, however,  by  the  power  of  the  deposited  carbon  to  reduce 
oxide  of  iron  at  all  temperatures  above  720  degrees  F.  This 
fact  and  the  action  of  carbon  in  changing  CO2  to  CO  at  all  tem- 
peratures above  710  degrees  prevents  the  decomposing  limestone 
from  undoing  the  work  which  the  CO  has  done  in  the  top  of  the 
furnace. 

Action  of  Deposited  Carbon — Carbon  which  has  been  depos- 
ited from  CO  at  low  temperatures  in  the  top  of  the  furnace  may  be 
carried  downwards,  dissolved  by  CO2  and  pass  upward  in  the 
form  of  CO  again,  only  to  be  redeposited  before  escaping;  from 
the  furnace  and  brought  once  more  into  the  region  of  the  carbon 
transfer.  In  this  way  an  indefinite  cycle  may  occur.  The 
activity  of  CO2  in  attacking  deposited  carbon,  however,  must 
not  be  considered  an  unmitigated  evil,  since  it  tends  to  remove 
what  may  become  a  serious  obstruction  to  the  passage  of  the 
gases.  The  net  result  of  this  reaction  is  that  we  find  very  little 
CO2  in  the  gases  at  a  temperature  above  760  degrees  F.  On 
the  other  hand,  the  action  permits  comparatively  little  of  the 
deposited  carbon  to  reach  the  hearth.  Carbon  deposition  ceases  at 
900  degrees  F.,  and  from  that  point  to  the  hearth  it  is  subject 
to  the  continuous  attacks  of  CO2,  and  residual  oxygen  of  the 
ore,  and  may  also  supply  some  of  the  impregnated  carbon  of 
the  pig, 


Action  Within  the  Furnace.  191 

Summary. — These  inter-reactions  may  be  conveniently  sum- 
marized as  follows : 

400  degrees  P.  and  upward — CO  reduces  oxides  of  iron  with  the  formation  of  CO2, 
which  is  permanent. 

Fe2Q3  +  SCO  —  2Fe  +  3CO2. 

480  degrees   F.   to  900  degrees   F. — CO   is   decomposed  by   the   sponge  and   lower 
oxides,  carbon  is  deposited  and  CO2  formed,  which  is  permanent. 

2CO  4-  Fex  =  Fex  4-  C  -4-  CO2. 
710  degrees  F.  and  upward — CO2  attacks  solid  carbon,  forming  CO. 

C02  +  C  =  2CO. 

720  degrees  F.  and  upward — Solid  carbon  reduces  oxides  of  iron  with  formation 
of  CO. 

C  +  FeO  =:  Fe  +  CO. 

760  degrees  F.  and  upward — CO2  oxidizes  metallic  sponge,  with  the  formation  of 
CO. 

C02  +  Fex=  FexO  +  CO. 

1100  degrees   F.   and   upward — CaCO»  is   decomposed   with   the   evolution   of  CO2, 
which  is  at  once  resolved  into  CO. 

CaC03  ==  CaO  +  CO2. 

From  these  facts,  certain  obvious  conclusions  may  be  drawn : 

(1)  CO  can  never  wholly  reduce  Fe2O3  to  the  metallic  state. 
The  reduction  is  always  accompanied  by  the  evolution  of  CO2, 
which  partly  neutralizes  the  action  of  the  CO.     For  example, 
Bell  found  that  Fe2O3  and  iron  sponge,  acted  upon  simultaneously 
by  pure  CO   for  five  hours  at  red  heat,  each   contained  at  the 
end,  i  per  cent,  of  the  O  necessary  to  form  Fe2O3.     The  presence 
of  the  CO2   from   reduction  in  the  one    case    and    the    carbon 
deposition  in  the  other,  was  sufficient  to  maintain  such  a  residue 
of  oxygen. 

(2)  It  is  evident  that  for  every  mixture  of  CO  4-  CO2  at  a 
given  temperature,  or  for  every  temperature^of  the  given  mixture 
there  is  a  definite  point  of  equilibrium    below    which    reduction 
cannot  go,  or  beyond  which  oxidation  cannot  occur.     Thus  Bell 
found  that  when 

CO  +  CO2  acted  on  ore  for  several  hours  at  bright  red 28.65  %  O  remained. 

When  CO  4-  CO2  acted  on  spongy  iron  for  several  hours  at 

bright  red 28.50  %  O  remained. 

Which  shows  equilibrium  point  for  equal  parts  of  CO  and  CO2. 

When  2CO  4-  CO2  acted  on  ore  for  six  hours  at  low  red 37.0    %  O  remained. 

When  3CO  +  CO2  acted  on  same  ore  for  six  hours  at  low  red.  .13.5    %  O  remained. 

Which  shows  that  the  point  of  equilibrium  varied  with  the  gas  mixture. 

(3)  When  a  point  of  equilibrium  is  reached,  an  increase  of 
temperature   or   an    increase   of   CO2   will   oxidize    the   product, 
while  a  decrease  of  either  will  have  the  opposite  effect.     Hence, 


192 


Blast  Furnace. 


Action  Within  the  Furnace.  193 

since  it  is  desirable  from  a  point  of  fuel  economy  to  have  the 
ratio  of  CO  to  CO2  as  low  as  possible,  the  top  temperature  should 
be  kept  low  to  counteract  the  oxidizing  effect. 

(4)  Since  carbon  is  deposited  at  low  temperatures,  and  its 
reducing  effect  is  not  diminished  by  high  temperatures,  we  have 
a  means  of  reducing  the  last  traces  of  oxygen  which  are  not 
removed  by  CO  in  the  presence  of  CO2. 

The  changes  which  take  .place  in  the  materials  at  various 
depths  and  temperatures  while  passing  through  the  furnace  have 
been  platted  graphically  by  Dougherty  as  shown  on  page  192. 

This  plate  is  very  instructive  in  that  it  enables  the  eye  to  help 
the  brain  grasp  the  various  simultaneous  changes  which  take 
place,  but  it  is  constructed  from  assumptions  not  entirely  in 
accord  with  those  usually  accepted.  The  tuyere  temperature  given 
as  1500  degrees  C.  has  generally  been  observed  to  be  above  1900 
degrees  C.  At  a  depth  of  19  feet  the  ore  is  given  as  entirely  in 
the  state  of  FeO,  which  implies  that  only  one-third  of  the  oxygen 
has  been  removed  at  that  depth,  thus  Fe2O3  =  2FeO  +  O, 
whereas  Bell  has  shown  that  fully  85  per  cent,  is  removed  during 
the  first  ten  or  twelve  feet.  Moreover  the  diagram  shows  no 
metallic  iron  before  the  depth  of  26  feet,  while  Bell  found  metal 
above  10  feet  depth.  Bell  states  also  that  carbon  deposition  ceases 
at  red  heat  and  owing  to  the  action  of  CO2  little  or  none  reaches 
the  bosh,  but  the  diagram  indicates  that  it  persists  even  down  to 
the  tuyeres.  The  decomposition  of  limestone  is  here  represented 
as  sudden  and  complete  at  a  depth  of  32  feet,  at  which  point  the 
CO2  column  has  its  origin,  whereas  Bell's  analyses  showed  the 
presence  of  CO2  and  undecomposed  limestone  at  depths  of  60  to 
70  feet.  Bell's  analyses  also  show  that  cyanides  disappear  com- 
pletely from  the  gases  before  they  have  risen  45  feet  from  the 
tuyeres. 

THE  CARBON   RATIO. 

A  fair  average  composition  by  volume  of  the  gases  which 
escape  from  a  blast  furnace  is  as  follows : 

co.  co,.  H.  CH,.  N. 

24.5  12.0  1.25  0.25  62.0 

It  was  formerly  believed  that  the  ratio,  ==-*  could  not  fall 
below  2,  and  proper  reducing  effect  in  the  furnace  be  maintained. 


194  Blast  Furnace. 

It  has  been  shown  repeatedly,  however,  that  a  furnace  can  be 
operated  successfully  for  considerable  periods  with  a  ratio  of  1.35 
or  less.  This  ratio  of  the  unsaturated  to  the  saturated  carbon 
in  the  gases  is  of  vital  importance  to  the  fuel  economy.  The 
heat  liberated  by  the  combustion  of  i  pound  of  carbon,  when 
burned  to  the  state  of  complete  oxidation,  is  14,550  B.  T.  U.,  while 
that  liberated  by  the  unsaturated  compound  is  only  4450  B.  T.  U. 
per  pound.  Since  over  three  times  the  heat  is  produced  by  the 
combustion  to  CO2,  it  follows  that  the  greater  the  proportion  of 
CO2  in  the  gases,  the  more  efficiently  each  pound  of  fuel  has  done 
its  duty,  and  the  less  fuel  will  be  needed  to  keep  up  the  furnace 
temperature.  The  importance  of  the  carbon  ratio  to  fuel  con- 
sumption may  be  easily  calculated : 

Ratio  CO  to  COo  1.85  =  (0.65  X  4450)   -f   (0.35  X  14,550)  =  7985  B.  T.  U.  per 

unit  C. 
Ratio  CO  to  CO;,  2.33  —  (0.70  X  4450)  +  (0.30  X  14,550)  =  7480  B.  T.  T'.  i>:>r 

unit  C. 
Decrease  per  pound  carbon  in  quantity  of  heat  development  ~  505  =  6  per  cent.  C. 

which  must  be  made  up  by  burning  additional  fuel,  which  in 
turn,  is  less  effective,  on  account  of  being  less  completely 
oxidized. 

Quantity  of  CO  and  CO2 — While  the  ratio  of  CO  to  CO, 
varies  with  the  fuel  consumption,  it  should  be  observed  that  the 
quantity  of  CO2  per  100  pounds  of  pig  is  practically  constant. 
This  becomes  self-evident  when  it  is  recalled  that  the  CO.  results 
entirely  from  the  addition  of  oxygen  in  the  reducing  zone  to 
the  CO  from  the  hearth.  The  total  quantity  of  oxygen  to  be 
extracted  from  the  ore  per  100  pounds  of  pig  varies  within  very 
narrow  limits,  and  can  never  be  very  far  from  43  to  44  pounds. 
Since  only  about  90  per  cent,  of  the  reduction  is  accomplished  by 
the  gases,  it  follows  that  about  39  pounds  of  oxygen  per  IOG 
pounds  of  pig  will  usually  be  taken  up  by  the  gases.  This 
quantity  of  oxygen  demands  about  29  pounds  of  carbon,  from 
which  it  appears  that  the  quantity  of  carbon  existing  in  the  gases 
as  CO2  will  never  be  far  from  29  to  30  pounds  for  each  TOO 
pounds  of  pig.  Consequently,  the  ratio  will  depend  solely  upon 
the  variation  in  CO.  It  is  evident,  therefore,  that  each  rate 
of  fuel  consumption  will  be  characterized  by  a  different  but 
tolerably  definite  carbon  ratio.  For  a  given  set  of  conditions  this 


Action   Within  the  Furnace. 


195 


ratio  may  be  calculated  approximately  from  the  fuel  consumed. 
The  problem  involves  three  factors :  the  carbon  in  the  fuel  used, 
the  carbon  added  by  the  limestone  and  the  carbon  withdrawn 
by  carbon  impregnation.  The  algebraical  sum  of  these  factors, 
less  29,  gives  the  weight  of  carbon  as  CO. 

Variations  in  Carbon  Ratio — If  we  assume  that  5.7  pounds 
carbon  is  added  per  100  pounds  pig  by  the  use  of  50  pounds 
stone,  and  that  3.4  pounds  carbon  enters  the  pig,  making  a  net 
addition  of  2.3  pounds,  then  the  carbon  ratio  for  various  fuel 
consumptions  may  be  found  as  follows : 


Fuel  con- 
sumption pci- 

Pounds  C 

Net  addition 

lon  pig  coke, 

from  fuel 

C  of  stone, 

85  %  fixed  C., 

per  100 

less  that  im- 

Total C 

Carbon 

pounds. 

pounds  pig. 

pregnated. 

in  gases. 

C  as  CO2. 

C  as  CO. 

ratio. 

1,700 

64.51 

2.30 

66.81 

29 

37.81 

1.31 

1,800 

68.34 

2.30 

70.64 

29 

41.64 

1.44 

1,000 

72.08 

2  30 

74.38 

29 

45.38 

1.57 

2,000 

75.80 

2.30 

78.10 

29 

49.10 

1.70 

2,100 

79.69 

2.30 

81.99 

29 

52.99 

1.83 

2,200 

83.47 

2.30 

85.77 

29 

56.77 

1.96 

2,300 

87.30 

2.30 

89.60 

29 

60.60 

2.09 

2,400 

91.07 

2.30 

93.37 

29 

64.37 

2.22 

2,500 

94.86 

2.30 

97.16 

29 

68.16 

2.35 

2,600 

98.60 

2.30 

100.90 

29 

71.90 

2.48 

2,700 

102.42 

2.30 

104.72 

29 

75.72 

2.61 

2,800 

106.25 

2.30 

108.55 

29 

79.55 

2.74 

2,000 

110.07 

2.30 

112.37 

29 

83.37 

2.87 

3,000 

113.81 

2.30 

116.11 

29 

87.11 

3.00 

CHEMICAL  REACTIONS. 

Of  the  chemical  reactions  which  take  place  in  the  furnace, 
seven  may  be  distinguished  as  being  persistent  and  authentic. 
Of  the  seven,  three  may  be  grouped  together  as  being  heat-giving, 
or  exothermic,  and  four  as  heat-absorbing,  or  endothermic. 

Exothermic  Reactions. — The  exothermic  reactions  are  as 
follows : 

(1)  Oxidation   of   carbon   to   carbon   monoxide   by   the   free 
oxygen  of  the  blast  and  the  residual  fixed  oxygen  of  the  ore, 
thus,  2C  +  O2  =  2CO,  DV  which  there  is  developed  4450  B.  T.  U. 
per  pound  of  carbon. 

(2)  Oxidation  of  part  of  the  carbonic  monoxide  to  carbonic 
dioxide  through  reduction  of  the  iron  of  the  ore,  thus,  Fe,O3  + 


136  Blast  Funiacc. 

3CO  =  2Fe  -j-  3CO2,  by  which  there  is  developed  10,100  B.  T. 
U.  per  pound  of  carbon. 

(3)  Oxidation  of  another  portion  of  the  carbonic  monoxide 
to  carbonic  dioxide  through  the  deposition  of  carbon,  thus, 
2CO  =  C  -f-  CO2,  by  which  there  is  developed  10,100  —  4450  = 
5650  B.  T.  U.  for  each  pound  of  carbon  so  oxidized. 

Endothermic  Reactions — The  endothermic  reactions  are  as 
follows : 

(1)  The   decomposition   of   limestone   into   lime   and   carbon 
dioxide,    thus:    CaCO3    =    CaO    +    CCX,    which    absorbs    812.7 

B.  T.  U.  per  pound  of  stone  or  -  =  6772.5  B.  T.  U. 

per  pound  of  carbon  in  the  stone. 

(2)  The    reduction  of    carbonic  dioxide    by    carbon,    thus: 
CO2  +  C  =2CO,  thereby  absorbing  14,550  --  (2  X  4450)   - 
5650  B.  T.  U.  for  each  pound  of  carbon  reduced. 

(3)  Reduction  of  carbonic  dioxide  by  metallic  iron     or  the 
lower  oxides  of  iron,  thus :  CCX  +  xFe  =  FexO  +  CO,  absorbing 
14,550  —  (6300  +  4.450)  —  3800  B.  T.  U.  per  pound  of  carbon 
involved. 

(4)  Decomposition  of  moisture  into  its  elements,  thus:  C  -j- 
H,O   =   CO   +   H2,  thereby  absorbing  6890  -  -  2965   =   3925 
B.  T.  U.  per  pound  water,  or  5885  B.  T.  U.  per  pound  of  carbon 
involved. 

Reduction — The  reduction  of  oxides  of  iron  by  carbon  may 
take  one  of  three  forms: 

(i)     3C  +  Fe203  =  2Fe  +  3CO, 

12 

which  liberates  4450  B.  T.  U.  per  pound  carbon,  or  4450  X  — z- 

—  3337  B.  T.  U.  per  pound  oxygen  removed,  and  7335  absorbed, 
a  loss  of  3997  B.  T.  U. 

(2)  3C  +  2Fe203  =  4Fe  +  3CO2, 

12 

which  liberates  14,550  B.  T.  U.  per  pound  carbon,  or  14,550  X  — 

=  5455  B.  T.  U.  per  potmd  oxygen  removed  and  7335  absorbed, 
a  loss  of  1880  B.  T.  U. 

(3)  3CO  +  Fe203  =  2Fe-+  3CO2, 

which  liberates  4330  B.  T.  U.  per  pound  CO,   or  4330   X  — z 


Action  Within  the  Furnace.  197 

=  7577  B.  T.  U.  per  pound  oxygen  removed  and  7335  absorbed, 
a  gain  of  242  B.  T.  U. 

The  last  reaction  gives  the  most  heat  per  unit  of  oxygen,  and 
hence  is  most  desirable  from  the  standpoint  of  heat  development. 
Moreover,  it  is  exothermic,  and  when  once  begun  is  capable  of 
running  without  further  additions  of  heat. 

Zones  cf  Reduction — As  we  have  seen,  the  action  of  CO  in 
the  top  of  the  furnace  removes  the  bulk  of  the  oxygen  from  the  ore 
before  it  has  descended  far.  Bell  found  in  his  researches  that 
from  certain  ores,  76  per  cent,  of  the  oxygen  had  been  removed 
at  a  depth  of  10  feet  and  18  per  cent,  still  remained  at  70  feet, 
With  the  Lake  ores  in  this  country,  however,  there  is  good  reason 
for  believing  that  fully  90  per  cent,  of  the  oxygen  is  removed  in 
the  upper  zone  of  reduction,  and  that  the  ore  undergoes  little 
change  beyond  heat  absorption  between  the  depth  of  20  feet  and 
the  zone  of  fusion.  In  the  lower  part  of  the  furnace,  however, 
there  is  a  second  zone  of  reduction,  where  the  metalloids  are  de- 
oxidized and  the  last  traces  of  oxygen  are  removed  from  the  iron. 

HEAT  DEVELOPMENT    IN   THE   FURNACE. 

The  heat  developed  in  the  furnace  may  be  ascertained  with 
tolerable  accuracy  if  the  quantity  and  analysis  of  the  escaping  gases 
are  known.  It  will  evidently  be  the  weight  of  carbon  burned  to 
CO2,  multiplied  by  14,550,  plus  the  weight  of  carbon  burned  to 
CO,  multiplied  by  4450.  It  is  only  necessary  to  ascertain  the 
quantity  of  these  gases  per  unit  of  iron.  ThilTcan  be  easily  done 
if  the  quantity  of  fuel  and  flux  and  the  composition  of  the  result- 
ing iron  are  known. 

Let  us  assume  an  iron  of  the  following  composition : 

Per  cent.  Per  cent. 

C 3.40  'S 0.05 

Si    1.50  Fe    94.00 

Mn    0.50 

P    0.50  99.95 

to  be  smelted  with  I  pound  of  coke  and  y?  pound  of  stone  for  each 
pound  of  pig,  and  that  the  slag  weighs  about  55  per  cent,  of  the 
iron.  Let  us  assume,  also,  that  the  coke  contains  85  per  cent, 
fixed  carbon  and  0.5  per  cent,  moisture  and  that  90  per  cent,  of 
the  oxygen  in  the  ore  is  removed  by  the  gases  in  the  upper  part 


198  Blast  Furnace. 

of  the  furnace,  leaving  the  other  10  per  cent,  including  that  com- 
bined with  the  metalloids,  to  be  removed  by  solid  carbon.  Let 
us  assume,  also,  as  a  fair  average,  that  it  takes  1.7  tons  of  ore 
to  make  a  ton  of  pig  containing  94  per  cent,  metallic  iron,  and 
that  the  ore  contains  3  per  cent,  combined  water  and  7  per  cent, 
moisture,  giving  5.1  and  11.9  pounds,  respectively,  of  water  per 
100  pounds  of  pig,  and  that  the  limestone  and  coke  each  contain 
0.5  per  cent,  moisture,  yielding  0.25  pounds  and  0.5  pounds  more 
water. 

In  order  to  ascertain  the  quantity  of  heat  developed  in  the 
furnace,  it  is  necessary  to  find,  first,  how  much  carbon  is  burned 
with  heating  effect,  then  how  much  is  changed  from  CO  to  CO2 
by  reduction  in  the  furnace  top.  The  rest  will  be  the  CO. 

The  oxygen  to  be  removed  from : 

Pounds. 
04.0  pounds  Fe  = 40.30 

3.4  pounds  C    = 0.00 

1.5  pounds  Si  — 1.71 

0.5  pounds  Mn    - 0.29 

0.5  pounds  P   = 0.65 

0.05  pounds  S  = 0.05 

09.95  pounds  pig  iron  —. 43.00 

Total  oxygen  to  be  removed  — 43.00 

90  per  cent,  removed  by  CO  = 38.70 

Leaving  to  be  removed  by  solid  C 4.30 

100  pounds  coke  at  85  per  cent,  fixed  carbon  = 85.0 

C  impregnated   in   pig 3.4  pounds. 

C  stolen  by  CO2  from  50  pounds  stone 5.7  pounds. 

9.1 

C  loft   to  be  burned 75.9 

C  burned  by  4.3  pounds  fixed  0 3.23 


C  left  to  be  burned  by  the  blast 72.67 

The  COs  in  the  gases  is  all  formed  by  the  action  of  CO  upon  the  ore, 
from  which  it  takes  up  90  per  cent,  of  the  oxygen,  or  38.7  pounds. 

12 

The  quantity  of  carbon  which  can  take  up  38.7  pounds  O  is  —  X  38.7  =  C 

16 

as  CO2  - 29.00 

C  burned  to  CO  by  the  blast  and  remaining  as  CO  — 43. G7  pounds. 

C  burned  to  CO  by  fixed  oxygen  — 3.23  pounds. 

C    as   CO    = 46.90 

Total  carbon  consumed  as  above 75.90 

The  heat  development  of  the  furnace  may  now  be  shown  as 
follows : 


Action  Within  the  Furnace.  190 

B.  T.  U. 

29.0  pounds  C  burned  to  CO2,  releasing  14,550  B.  T.  U  = 421,950 

46.9  pounds  C  burned  to  CO,  releasing  4,4.10  B.  T.  U.  = 208,705 

Total  beat  development  by  fuel  = 630,655 

Less  heat  absorbed  by   reduction   of  5.7  pounds   C  from 

COo  to  CO  at 10,100  B.  T.  U. 

And  oxidation  simultaneously  of  5.7  pounds  C  from  C  to 

CO    at. .  4,450  B.  T.  U. 


Leaving  a  net  loss  of 5,050  B.  T.  U.  =.    32,205 

Whence  the  net  heat  development  in  the  furnace  ~ 598,450 

75.9  pounds  C  burned  to  CO2  develops   1,104,345 

which  shows  that  the  heat  development  in  the  furnace  is  54.2 
per  cent,  of  the  theoretical,  or  7885  B.  T.  U.  per  pound  carbon,  of 
which  66.9  per  cent,  is  due  to  CO2,  and  33.1  per  cent  to  CO. 

A  further  analysis  of  these  figures  shows  that  the  heat  de- 
veloped in  the  hearth  consists  of : 

B.  T.  U. 

75.9  pounds  C  burned  to  CO  at  4.450  B.  T.  U.  per  pound  — 337,755 

while  that  developed  in  the  furnace  top  consists  of  29.0  pounds  C  as  CO 

burned  to  CO2,  at  10,100  B.  T.  U.  per  pound  = 292,900 

630,655 
Less  the  heat  absorbed  by  carbon  transfer 32,205 

Net  heat  developed  as  above 598,450 

of  which  53.5  per  cent,  is  developed  in  the  hearth,  and  46.5  per 
cent,  in  the  top  of  the  furnace. 

Carbon  Ratio — In  order  to  find  the  carbon  ratio  existing  in 
the  final  gases,  it  is  necessary  to  take  into  account  the  carbon 
from  the  stone,  and  that  stolen  by  it,  as  follows: 

C  burned  to  CO  and  remaining  CO 46.9 

C  existing  as  CO  from  the  CO2  of  stone 5.7 

C  existing  as  CO,  stolen  by  CO2  of  stone 5.7 

58.3 
CO      58.3 

The  carbon  ratio  — =  2.01. 

COi     29.0 

Heat  in  the  Blast — In  addition  to  the  heat  developed  by  com- 
bustion, in  the  furnace,  there  is  another  source  of  heat  to  the 
hearth,  namely  the  heat  in  the  blast.  The  quantity  so  introduced 
often  amounts  to  one-fifth  of  the  total  heat  development  in  the 
furnace  and  one-third  of  that  developed  in  the  hearth.  It  may  be 
determined  by  multiplying  the  weight  of  the  air  by  its  specific 


200  Blast  Furnace. 

heat.    The  weight  of  the  blast  needed  by  the  fuel  per  100  pounds 
of  pig  may  be  found  as  follows  : 

Pounds. 

O2  needed  to  form  CO  with  7-.G7  pounds  carbon  = 96.89 

O2  furnished   by   moisture   in   blast    (annual   average,    3.7   grains   IIL»O   per 

cubic   feet   air)    = 2.50 


O2  furnished  by  dry  air  =• 9.4.39 

N2  accompanying  Oo  of  dry  air  — 310.55 

H2  accompanying  2.50  pounds  O2  in  moisture  — 0.31 

Total  weight  of  moist  blast  — 407.75 

which  at  60  degrees  F.  equals  5300  cubic  feet  per  100  pounds  of 
pig.  Owing  to  clearance  and  losses,  this  usually  requires  5500 
cubic  feet  piston  displacement. 

The  heat  brought  in  by  the  blast  may  be  determined  by  means 
of  the  formula: 
Heat  =  [0.2335  (*—?)  +  0.0000208  (t-—  t'2)]  X  weight  of  air. 

Between  60  and  1200  degrees  F.,  the  available  heat  in  the 
blast  per  100  pounds  pig  is  as  follows: 

407.75  pounds  [0.2335  X  1140  +  0.0000208  X  1,436,400] 

=  120,720  B.  T.  U. 
Based  on  the  total  heat  developed  in  the  furnace,  this  equals: 

120,720  X  100 

-  =  20.2  per  cent. 
598,450 
Based  upon  the  heat  developed  at  the  tuyeres,  it  equals: 

120,720  X  100 

£- — — =  77.7  per  cent. 

72.67  X  4450 

Temperature  of  the  Hearth — The  approximate  temperature  of 
the  hearth  may  be  calculated  from  the  total  heat  present  at  the 
tuyeres,  if  the  weights  and  specific  heats  of  the  products  of  com- 
bustion are  known.  The  weight  of  gases  which  results  from  the 
combustion  of  72.67  pounds  carbon  to,  the  condition  of  CO 
through  the  agency  of  moist  air,  is  as  follows : 

CO  '. : .  .169.56  pounds. 

Na  310.55  pounds. 

H2  0.31  pounds. 

480.42  pounds. 

which  is  equal  to  6.6 1  pounds  per  pound  of  carbon  burned  by 
the  blast.  The  specific  heats  of  N2  and  CO  are  the  same,  and 
that  of  the  small  quantity  of  H2  may  be  neglected.  The  total 


Action  Within  the  Furnace.  201 

quantity  of  heat  present  at  the  tuyeres  is  manifestly  that  de- 
veloped by  the  combustion  of  the  carbon,  plus  that  brought  in 
by  the  materials  of  combustion,  thus : 

B.  T.  U. 

Heat  developed  by  combustion  per  pound  carbon  rr 4,450 

120,720 

Heat  brought  in  by  blast  per  pound  carbon  —     —  — 1,661 

72.67 
Heat  brought  in  by  C  per  pound  carbon  — 0.5*  —     216 

Total  heat  present  in  the  hearth  = 0.5*  +  5,895 

Deducting  that  rendered  latent  in  decomposing  2.81  pounds  moisture 
2.81  X  5,750 


222 


72  67 


Net  heat  present  in  hearth  - 0.5*  +  5,673 

Substituting  these  values  in  the  formula  (0.2405*  +  0.00002143*2 
=  total  heat)  gives  6.61  (0.2405*  +  0.00002143*2)  —  0.5*  +  5,673, 
whence  1.5897*  +  0.00014165*2  =  0.5*  +  5,673  and,  0.00014165*2 
+  1.0897*  =  5,673. 

Completing  the  square  and  solving  for  *  gives, 
0.011 9*  =  42.3 

f  =  3,555  degrees  F. 

This  calculation,  however,  takes  no  note  of  the  heat  extracted 
from  the  hearth  walls  by  radiation  and  cooling  water.  This 
action,  which  is  exceedingly  difficult  to  measure  quantitatively, 
reduces  the  total  quantity  of  heat  present,  and  would  make  the 
result  somewhat  lower.  The  temperature  observed  by  Le  Chate- 
lier  was  3506  degrees  F. 

From  a  critical  survey  of  the  above  calculation,  it  is  evident 
that  the  weight  of  the  products  of  combustion  is  always  directly 
proportional  to  the  weight  of  carbon,  and  will  always  be  about 
6.6  pounds  per  pound  of  carbon.  For  a  given  set  of  conditions, 
therefore,  the  temperature  of  the  hearth  is  in  equilibrium,  no  mat- 
ter how  much  fuel  is  burned..  The  temperature  will  always  be 
that  of  combustion  under  the  given  conditions.  If,  however,  the 
conditions  be  changed,  the  equilibrium  will  be  destroyed  and  a 
new  temperature  of  combustion  will  result.  For  example,  if  the 
temperature  of  the  blast  be  increased,  or  its  percentage  of  mois- 
ture be  decreased  or  coke  at  a  higher  temperature  be  precipitated 
into  the  hearth,  a  higher  hearth  temperature  will  follow.  The 
maximum  temperature  is  usually  found  three  or  four  feet  above 
the  tuyere  zone. 

It  should  be  observed  here  that  the  above  temperatures  mark 
the  thermal  state  of  the  gases  and  not  that  of  the  products  of 


202  Blast  Furnace. 

fusion.  Since  the  latter  derive  their  heat  from  the  former  there 
must  necessarily  be  a  considerable  difference  of  temperature  in 
order  that  there  may  be  appreciable  interchange  of  heat  during 
their  brief  contact  as  they  travel  in  opposite  directions.  It  is 
probable,  therefore,  that  there  is  a  constant  difference  of  at  least 
300  to  400  degrees  F.  between  the  two  currents  at  any  given  level 
of  the  furnace. 

Zone  of  Fusion.. — Since  no  smelting  reactions  take  place  at  the 
tuyeres,  the  temperature  at  that  place  is  of  secondary  importance, 
The  really  important  point  in  the  heat  zone  is  the  zone  of  fusion, 
as  it  is  there  that  the  products  of  the  operation  are  subjected  to 
temperatures  which  give  them  their  distinctive  characteristics. 
Since  the  products  of  the  zone  of  fusion  melt  at  quite  different 
temperatures,  and  therefore  the  respective  points  at  which  the 
meltings  occur  are  necessarily  separated  by  an  appreciable  dis- 
tance, the  zone  of  fusion  must  be  looked  upon  as  a  wide  band,  or, 
better  still,  as  two  distinct  zones,  one  above  the  other.  The  locat- 
ing of  these  two  zones  in  the  furnace  is  not  a  simple  matter,  as 
they  are  subject  to  so  many  conditions  and  may  fluctuate  even 
within  comparatively  brief  periods.  The  factors  which  contribute 
most  to  this  uncertainty,  aside  from  the  quantity  of  heat  devel- 
oped by  combustion,  are:  the  degree  of  expansion  of  the  gases, 
the  latent  heat  of  fusion  of  the  products,  the  increase  of  specific 
heats  of  the  products.  The  last  two  are  accurately  known  quan- 
tities, but  the  first  evidently  depends  upon  the  bosh  angle  and  the 
position  of  the  zone  of  fusion.  If  it  is  assumed,  for  example,  that 
the  bosh  is  low,  and  its  area  does  not  greatly  exceed  twice  the 
hearth  area,  it  might  be  presumed  that  by  the  time  the  gases  have 
reached  the  slag-melting  zone,  they  have  lost,  through  cooling  and 
increased  space,  about  one-quarter  of  their  expansive  force.  As 
we  shall  see  later,  the  heat  that  would  be  absorbed  during  free 
expansion  per  100  pounds  of  pig  is  about  80,000  B.  T.  U.  Hence, 
under  this  supposition,  20,000  B.  T.  U.  would  be  absorbed,  or 
275  B.  T.  U.  per  pound  of  carbon  burned.  The  latent  heat  of 
fusion  of  slag  per  pound  is  about  180  B.  T.  U.  Assuming  55 

180  X  0.5 S 
pounds  of  slag  per  100  pounds  of  iron,  we  will  have : — '-— 

=  136  B.T.  U.  per  pound  of  carbon  burned.    The  specific  heats 


Action  Within  the  Furnace.  203 

of  CaO  and  SiO2  average  about  0.18  +  O.OOOO4/,  which  at  3000 
degrees  equals  about  0.30  B.  T.  U.  per  pound.  The  heat  capacity 
of  molten  iron  is  0.22  B.  T.  U.  per  pound,  and  of  carbon  it  is 

2 16 
0.5  —   — — -  B.  T.  U.  per  pound.    Allowing  for  the  heat  absorbed 

in  raising  the  temperature  of  these  substances  400  degrees,  and 
that  rendered  latent  by  expansion  of  gas  and  fusion  of  slag,  the 
formula  for  the  temperature  would  be  modified  to  read  as  follows : 

0.61    (0.2405*  +  0.00002143*2)   +   (1.367  X  0.22  X  400)   -4-   (0.76  X  0.30  X  400) 
+    (  0.5  -  ,-^~  )    X  400  rr  0.5*  +  5,673  -  (275  +  136), 

whence 

0.00014165*2  +  1.5897*  +  120  +  91  +  171  =  0.5*  +  5,673  —  411. 
Transposing  gives 

0.00014165*2  +  1.0897*  =  4,880, 
completing  tUe  square, 

0.00014165*2  4-  1.0897*  +  2,097  =  6,977. 
Taking  square  root, 

0.0119*  +  45.8  =  83.5. 
0.0119*  =  37.7 

*  -  3,170  degrees  F. 

which  is  the  temperature  of  the  gases  at  the  level  of  slag  fusion. 
Deducting  about  350  degrees,  for  difference  of  temperature,  gives 
2820  degrees  F.  as  the  melting  point  of  the  slag. 

By  carrying  the  same  reasoning  a  step  farther  we  may  investi- 
gate the  zone  of  fusion  of  the  iron.  Assuming  that  the  gases  have 
lost  another  quarter  of  their  expansive  force,  the  additional  latent 
heat  of  expansion  performed  of  carbon  would  be  275  B.  T.  U. 
The  latent  heat  of  fusion  of  iron  is  126  B.  T.  U.  per  pound,  hence 

1 26 
per  pound  of  carbon  it  will  be ^-  =  173  B,T.  U.    Deducting 

these,  together  with  the  heat  necessary  to  raise  the  temperature 
of  the  molten  iron,  the  slag  forming  materials  and  the  coke  an- 
other 400  degrees,  we  have  this  formula : 

6.61   (0.2405*  +  0.00002143*2)  +   (1.367  X  0.22  X  800)   +   (0.76  X  0.30  X  800) 
+  (   0.5  -  -j^-Q  )      800  =  0.5*  +  5,673  -  (411  +  488) 

Which  equals 

0.00014165*2  -{-  1.5897*  +  240  +  182  4-  272  =  0.5*  +  5,673  —  899 
Transposing  gives 

0.00014165*2  +  1.0897*  =  4,080. 
Completing  square, 

0.00014165*2  +  1.0897*  +  2,097  =  6,177, 
0.0119*  +  45.8  =  78.6. 

0.0119*  —  32.8. 
*  -  2,755  degrees  F. 


204 


Blast  Furnace. 


DEGREES  FAHRENHEIT 
Temperature  Gradient  of  Blast  Furnace. 


Action  Within  the  Furnace.  205 

which  is  the  temperature  of  the  gases  at  the  iron  melting  zone. 
Deducting  350  degrees  for.the  difference  of  current  temperatures 
gives  2400  degrees,  which  is  about  the  melting  point  of  semi- 
carburized  iron. 

The  temperature  gradient  of  the  furnace  from  hearth  to  top 
may  be  represented  by  the  accompanying  diagram,  which  is  a 
modification  of  Allen's. 

Heat  Evolved  by  Reduction — Between  the  zone  of  fusion 
of  the  iron  and  the  zone  of  gaseous  reduction  very  little  heat  is 
rendered  latent  beyond  that  absorbed  in  setting  free  CO2  of  the 
flux.  Through  this  long  distance  the  gases  lose  heat  mainly 
through  conduction  to  the  materials  of  the  charge,  and  therefore 
it  has  been  termed  the  zone  of  heat  interception.  When  the  zone 
of  reduction  is  reached,  the  gases  meet  a  slight  evolution  of  heat. 
The  amount  of  heat  evolved  at  this  point  is  the  excess  of  heat 
developed  by  the  oxidation  of  CO  to  CO2,  less  that  absorbe4  by 
the  reduction  of  Fe2O3  to  Fe2,  in  accordance  with  the  reaction, 
Fe203  +  3CO  ==  Fe2  +  3CO2. 

B.  T.  U. 

29  parts  C  as  CO  oxidized  to  CO2,  developing  10,100  B.  T.  U  - 292,900 

90.2  parts  Fe  reduced,  absorbing  3,143.5  B.  T.  U.  = 283,615 

Heat  liberated  per  100  pounds  pig  = 9,285 

Composition  of  Final  Gases — As  the  gases  pass  upward 
from  the  hearth,  they  make  the  following  additions  before  es- 
caping from  the  furnace: 

43.00  pounds  O  from  the  ore. 

3.23  pounds  C  burned  by  fixed  O. 
26.77  pounds  CO  due  to  carbon  transfer. 
17.75  pounds  moisture  and  combined  H2O  from  ore. 

90.75  pounds. 

Adding  these  to  the  gases  at  the  tuyeres  gives  the  composition  of 
the  escaping  gases,  as  follows : 

£O2    , , 106.40  pounds. 

CO 136.16  pounds. 

N2    310.55  poundss 

H2   0.31  pounds 

Steam 1 7.75  pounds. 

Total  weight  of  escaping  gases  per  100  pounds  pig 571.17  pounds. 

Temperature  Due  to  Reduction. — If  we  assume  that  the 
materials  and  the  products  of  combustion  absorb  all  of  this 


206  Blast  Furnace. 

heat,  it  is  a  simple  matter  to  calculate  the  resulting  rise  of  tem- 
perature, as  follows: 

Ore,  1.7   (0.1456*  +  0.000188*2)   = 0.2475*  +  0.0003196*2 

Coke,  1.0  (0.1567 1   f  0.00036/-)   - 0.1567  r  -}-  0.0003600*2 

Stone,  0.5  (0.20851)  = 0.1 04 1'/ 

CO2,  1.0G4    (0.187*  +  0.00011 1/2)    - 0.1990*  -f  0.0001181  J2 

N2  +  CO,  4.467   (0.2405*  +  0.00002143*2)   - 1.0743*  +  0.0000957/2 

H3O,  0.177    (0.42*  -f   0  000185.*2)    — 0.0743*  -f  0.0000327*2 


1.8560*+  0.0009261*2 
1.8560*  +  0.0009263  *2  =  92.85. 

Completing  the  square  gives 

0.0009261*2  -f  1.856*  +  930.5  —  1,023.35. 
Taking  the  square  root, 

0.03043*  +  30.5  =  32.0. 
Whence,  *  —  49  degrees  F. 

However,  there  is  not  sufficient  time  for  the  solid  products  to 
absorb  their  full  capacity  of  heat,  and,  therefore,  the  temperature 
of  the  gases  is  always  considerably  higher. 

Heat  Lost  in  Waste  Gases — The  heat  in  the  escaping 
gases  at  450  degrees  F.  may  be  calculated  by  means  of  the  for- 
mula for  difference  of  temperatures,  as  follows: 

B.  T.  u. 

CO2,  106.40  (0.187  X  390  -f  0.000111  X  198,900)  = .  .10,108 

£°'iift'iS!446-71  <  0.2405  X  390  +  0.00002143  X  198,900)  = 43,803 

JN»,  olu.OO  3 

H.,  0.31  .(3.367  X  390  +  0.0003  X  198,900)  = 425 

Steam,  17.75  (0.42  X  390  +  0.000185  X  198,900)  = 3.560 

57,896 

which  is  the  amount  of  heat  that  would  be  given  up  if  the  tem- 
perature were  brought  down  to  60  degrees  F.  This  heat  is 
equivalent  to  15  pounds  of  coke  burned  at  the  tuyeres  per  100 
pounds  pig  or  336  pounds  per  ton. 

HEAT  REQUIREMENT. 

The  heat  requirements  of  a  furnace  making  .a  given  grade  of 
pig  on  a  given  consumption  of  fuel  and  flux  would  be  constant, 
were  it  not  for  changes  in  the  weather,  which  introduce  varying 
amounts  of  moisture  into  the  furnace  by  means  of  the  blast  and 
materials  of  the  charge.  The  constant  heat  requirement  for 
manufacturing  100  pounds  of  pig  under  the  present  supposition 
may  be  stated  as  follows : 


Action  Within  the  Furnace. 


207 


B.  T.  U. 
Reduction  of  94.0  pounds  Fe  from  Fe2O3  @  ..................   3,143.5 

Reduction  of  1.5  pounds  fc>i  from   SiO2   @  ...................  11,571.5 

Reduction  of  0.5  pounds  Mn  from  MnO2  @  ..................   4,100.7 

Reduction  of  0.5  pounds  P  from  P3O5  @  ....................  10,605.6 

Reduction  of  0.05  pounds  S  from  SO«  @  ....................    3.896.0 

Reduction  of  0.25  pounds  Mn  from  MnO2  to  MnO  @  ..........    2,975.0 

Decomposition  of  5.1  pounds  II,O  of  hydration  of  ores  @  ......    1,300.0 

Decomposition  of  47.5  pounds  CaCO8  (from  50  pounds  stone)   @       812.7 
Reduction  of  5.7  pounds  C  as  CO-  to  CO  @  ..................  10,100.0 

Reduction  of  3.4  pounds  C  as  CO  to  C  @  ....................    4,450.0 

Fusion  of  100.0  pounds  pig  iron   @  .........................       666.0 

Fusion  of  55.0  pounds  slag  @  .............................    1,000.0 


Total  constant  requirement 


B.  T.  U. 

295,500 

17,357 

2,050 

5,303 

195 

744 

6,630 

38,603 

57,570 

15,130 

66,600 

:  55,000 

.560,682 


The  variable  heat  requirements  on  the  same 
basis  may  be  stated  as  follows  : 


Evaporation  of  0.50  pounds  moisture  in  coke 
Evaporation  of  0.25  pounds  moisture  in  stone 
Evaporation  of  11.90  pounds  moisture  in  ore  @ 
Decomposition  of  2.81  pounds  moisture  in  blast 
Carried   off   in   571.17   pounds   waste   gases    @ 
grees  F 


......  1,120.0=  560 

......  1,120.0  —  280 

.......  1,120.0  =  13,328 

@  .....  5,750.0=  16,157 

450   de- 

= 57,896 


Total  variable  requirement  .....  .  .............  ,  .  .  .  . 

Total  requirement  of  100  pounds  pig,  under  above  conditions 


88.221 
648,903 


Unavoidable  Losses  of  Heat  —  -By  comparing  the  heat  devel- 
opment and  the  requirements  of  the  furnace  per  100  pounds  of 
pig,  we  have  the  following: 

B.  T.  u. 

Net  heat  developed  in  furnace  by  fuel  .......    ........................  598,450 

Heat  brought  in  by  bl-ast  ......................................  .....  120,720 

Total  heat  available  ...........................................  719,170 

Total  heat  accounted  for..  ..648,903 


Leaving  unaccounted  for 


0,267 


which  amounts  to  about  9.77  per  cent,  of  that  available,  and  which 
is  irrecoverably  lost  through  radiation  from  the  furnace  stack  and 
conduction  through  the  foundations  and  cooling  water. 

Heat  Intercepted  by  Descending  Materials.  —The  quantity  of 
heat  usefully  intercepted  by  the  column  of  descending  materials 
will  evidently  consist  of  the  total  heat  available  in  the  hearth,  less 
that  which  escapes  through  radiation,  conduction,  etc.,  plus  that 
which  is  carried  away  in  the  waste  gases.  The  amount  of  heat 
so  returned  to  the  hearth  per  100  pounds  pig  may  be  calculated  as 
follows  : 


208  Blast  Furnace. 

B.T.  r. 

Heat  carried  away  in  waste  gases 57,806 

Tloat  lost  by  radiation  and  conduction 76,867 

Total  heat  lost  to  the  furnace 134,763 

Deduct  heat  developed  in  furnace  by  reduction 9.2S5 

Net  loss  of  heat  which  was  available  in  the  hearth 125,478 

Total  heat  developed  in  hearth  (75.9  pounds  C  to  CO) 337,755 

Heat  brought  in  by  blast 120,720 


Total  heat  present  in  the  hearth i58,475 

Absorbed  in  decomposing  2.31  pounds  moisture 16,157 

Not  amount  of  heat  available  in  hearth 442,318 

442,318 — 125,478  =  316,840  B.  T.  U.,  which  represents  the 
available  heat  intercepted  by  the  descending  materials.  Figured 
on  the  basis  of  the  total  heat  developed  in  the  hearth  this  equals : 

316,840  X  100 

-  —    69.1  per  cent. 

458,475 

The  heat  utilized  in  decomposing  the  moisture  of  the  blast  equals, 
16,157  X  100 

-  =    3.5  per  cent. 

458,475 

The  heat  irrecoverably  lost  to  the  furnace  equals, 
125,478  X  100 

-  —    27.4  per  cent. 

458,475 

This  shows  the  blast  furnace  to  have-  a  thermal  efficiency  of 
72^/2  per  cent. 

Effect  of  Heated  Blast — When  the  heated  blast  was  first 
introduced  it  was  found  that  it  was  accompanied  by  a  saving  of 
fuel  out  of  proportion  to  the  quantity  of  fuel  necessary  to  heat  it. 
This  was  not  understood  until  it  was  shown  that  the  combustion 
in  the  furnace  hearth  developed  only  30  per  cent,  of  the  heat  of 
the  fuel.  It  then  became  clear  that  the  blast,  when  heated  outside 
of  the  furnace  where  complete  combustion  of  fuel  can  take  place, 
requires  only  about  one-third  of  the  fuel  that  is  required  inside 
the  furnace.  In  additon  to  the  extra  fuel  needed  to  heat  the  blast 
inside  the  furnace,  there  is  an  increased  quantity  of  blast  needed 
to  burn  the  extra  fuel  to  be  heated,  and  a  correspondingly 
increased  loss  of  heat  carried  away  by  the  increased  quantity  of 
waste  gases.  The  quantity  of  coke  burned  to  CO  which  would 
produce  the  120,720  B.  T.  U.  in  the  blast  when  heated  to  1200  de- 
grees F.  is  -—-^ =-  85  —  32  pounds  for  each  100  pounds  of  iron. 


Action  Within  the  Furnace.  209 

When  we  take  into  account  the  increased  quantity  of  blast  needed 
to  consume  this  fuel,  which  must  also  be  heated,  and,  in  addition, 
the  losses  of  heat  due  to  the  increased  quantity  of  gases,  we  can 
see  at  a  glance  that  the  fuel  consumption  of  a  cold  blast  furnace 
may  easily  exceed  that  of  a  hot  blast  furnace  by  50  per  cent. 

Fuel  Value  of  Hot  Blast. — The  value  of  increase  in  blast 
temperature  in  terms  of  coke  illustrates  the  advantages  of  hot 
blast.  If  407.75  pounds  be  the  wreight  of  blast  needed  per  100 
pounds  of  pig,  then  the  quantity  of  heat  brought  into  the  fur- 
nace for  100  degrees  F.  of  blast  temperature  above  1200  degrees 
F.  may  be  found  by  the  formula  .2335  (t-tf)  +  .0000208  (tz-t'~) 
=  heat. 

4°7-75  (°-2335  X  100  +  .0000208  X  250,000)  =  11,640  B.  T. 

U.,  -  -^-85  =  3   pounds    coke,   burned    in   the   hearth    per 

100  pounds  of  pig  produced,  which  is  a  saving  of  about  70  pounds 
coke  per  ton  of  pig,  or  3  per  cent,  of  fuel.  A  decrease  of  3  per 
cent,  of  fuel  means  also  a  decrease  of  3  per  cent,  of  blast,  so  that 
the  quantity  of  heat  actually  brought  in  at  that  temperature  would 
be  somewhat  less  than  indicated. 

Minimum  of  Fuel — If  the  duty  of  the  fuel  were  simply  to 
furnish  a  reducing  agent  for  the  ore,  it  would  be  sufficient  to 
furnish  enough  carbon  to  remove  the  oxygen.  Assuming  that 
the  reduction  could  be  performed  by  solid  carbon  with  the  for- 
mation of  COo,  it  would  be  necessary  to  use  only  -  ^  ^  = 

4X5° 

16.05  pounds  C,  instead  of  100  pounds  in  order  to  make  100 
pounds  of  iron.  But  we  have  seen  that  a  large  excess  of  carbon 
in  the  gases  is  necessary  to  perform  the  reduction.  Moreover, 
the  carbon  does  not  burn  to  the  condition  of  CO2  in  the  furnace 
but  to  CO,  thereby  giving  out  only  about  30  per  cent,  of  its  avail- 
able heat.  This  would  appear  to  be  a  sad  waste  of  calorific 
energy,  were  it  not  for  the  fact  that  CO  is  indispensable  in  pre- 
paring the  ore  for  fusion,  and  moreover,  however  much  sensible 
heat  is  intercepted,  there  is  external  work  to  be  done  by  which 
this  undeveloped  energy  may  still  be  utilized.  Since  a  portion 
of  the  fuel  energy  is  released  in  the  zone  of  combustion  and  a 
still  further  quantity  in  the  zone  of  reduction,  it  is  evident  that 


210  Blast  Furnace. 

there  are  two  zones  of  heat  development,  of  which  the  greater 
is  in  the  lower  furnace  and  the  lesser  in  the  upper. 

Limits  of  Blast  Temperature.  —  Since  the  use  of  heated  blast 
is  so  effective  in  cutting  down  the  need  of  fuel  in  the  furnace, 
it  might  be  argued  that  if  the  blast  could  be  heated  sufficiently, 
the  iron  could  be  made  by  hot  air  alone.  Theoretically,  the  fuel 
could  be  replaced  by  the  hot  blast  down  to  the  16.05  pounds  of 
carbon  per  100  pounds  of  pig  that  we  found  necessary  to  perform 
the  reduction,  were  it  not  for  the  physical  difficulty  of  putting 
into  the  blast  the  required  quantity  of  heat.  As  the  quantity  of 
fuel  decreased,  a  constantly  less  quantity  of  blast  would  be 
needed,  and  therefore  each  particle  of  the  air  would  have  to  be 
heated  to  a  correspondingly  higher  temperature.  Assuming  the 
heat  requirement  of  the  furnace  to  be  as  found  above,  458,475 
B.  T.  U.  per  100  pounds  of  pig,  of  which  337,755  is  furnished 
by  the  combustion  of  76  pounds  C  to  CO,  and  120,720  by  407.75 
pounds  blast,  heated  to  1200  degrees  F.,  then  the  necessary  blast 
temperature  for  each  decrease  of  fuel  would  be  as  follows: 


Pounds  C 
Fuel  per  per  100 
ton  pig.  pounds  pig. 
2,240      76 
2,000      67 
1,800      60 
1,600      54 

Effect  of  Cold  Blast.  —  The  gases  which  are  given  off  by  a 
cold  blast  furnace  do  not  differ  materially  from  those  from  a  hot 

blast  furnace,  except  that  the  ratio   r  ^    is  higher,  as  a  result  of 


Tem- 

Heat 

Wt.          perature 

leat  require-       Heat  of 

needed 

air  to     necessary, 

ment.            combustion. 

in  blast. 

burn  0.    degrees  F. 

458,  47o              337,755 

120,720 

407.75             1,200 

458,475              208,150 

160,325 

359.80             1,650 

458,475              267,000 

191,475 

322.20             2,125 

458,475              240,300 

218,175 

290.00             2,600 

the  higher  fuel  requirement.  The  presence  of  more  CO  with  its 
attendant  nitrogen  gives  a  greater  volume  of  gases,  which  must, 
in  consequence  of  their  greater  volume,  pass  more  rapidly 
through  the  cold  stock,  thereby  being  less  thoroughly  cooled. 
The  smaller  the  quantity  of  gases,  the  more  slowly  they  need  to 
move  to  make  place  for  that  following,  and  consequently  the  more 
time  they  have  to  give  up  their  sensible  heat  to  the  surrounding 
materials. 

Volume  of  the  Blast  —  We  have  found  that  under  the  above 


Action  Within  the  Furnace.  211 

conditions,  407.75  pounds  of  air  enters  the  furnace  for  each  100 
pounds  of  pig,  which  corresponds  to  about  5300  cubic  feet  at  60 
degrees  F.  In  being  heated  to  1200  degrees  F.,  the  air  expands 
enormously;  its  volume  at  32  degrees  F.,  being  added  for  each 
rise  of  490.5  degrees  F.  The  old  volume  will  then  bear  to  the 
new  the  same  ratio  as  their  respective  absolute  temperatures. 
This  relation  may  be  expressed  as  follows : 

i    :  60  +  458.5  ==  x   :  1200  +  458.5, 

by  which  it  appears  that  the  new  volume,  x,  amounts  to  about 
3.2  cubic  feet  for  each  cubic  foot  at  60  degrees  F.  However,  as 
blast  pressure  in  modern  furnaces  usually  reaches  14  to  15  pounds 
per  square  inch,  or  about  one  atmosphere,  it  follows  that  the  ac- 
tual volume  of  the  blast  as  it  enters  the  furnace  will  be  about 
1.6  times  the  volume  of  the  air  at  60  degrees  F. 

The  piston  displacement  required  to  furnish  407.75  pounds 
of  blast  varies  considerably  at  different  seasons  of  the  year.  For 
example,  when  the  air  has  a  temperature  of  30  degrees  F.,  each 
pound  of  it  occupies  12.35  cubic  feet  of  space,  and  hence,  each 
100  pounds  of  pig  requires, 

40/75  X   12.35  --  5036  cubic  feet. 

At  90  degrees,  each  pound  of  air  has  a  volume  of  14.22  cubic 
feet,  and  hence  - 

4°7-75   X   14.22  =  5798  cubic  feet, 

which  are  required  for  the  same  purpose.  This  difference  of  762 
cubic  feet  represents  an  increase  of  over  15  per  cent,  in  volume, 
and  for  a  blowing  cylinder  84  x  60  inches,  requires  45  additional 
engine  revolutions  per  ton  of  pig  iron  made. 

It  is  customary  to  measure  the  quantity  of  blast  driven  into 
the  hearth  by  means  of  the  piston  displacement  of  the  engine. 
This  is  a  convenient  method,  but  it  is  only  approximate.  After 
clearance  space  is  deducted,  it  measures  with  tolerable  accuracy 
the  quantity  of  blast  that  leaves  the  cylinder  when  the  valves  are 
tight,  but  the  quantity  of  air  which  enters  the  furnace  will  be 
lessened  by  just  the  amount  of  leakage  between  the  engine  and 
the  hearth.  Good  connections  should  never  require  over  55  cubic 
feet  piston  displacement  per  pound  of  coke.  Since  the  quantity 
of  air  needed  by  the  furnace  is  absolutely  dependent  on  the  car- 
bon burned,  it  should  always  be  reckoned  in  terms  of  fuel.  Any 


212  Blast  Furnace. 

attempt  to  report  the  air  consumption  in  terms  of  iron  is  always 
indefinite,  unless  the  fuel  consumption  is  known,  since  the  quan- 
tity of  air  per  pound  of  pig  will  vary  according  to  the  fuel,  as 
follows : 

Fuel    consumption 1,800  \b.     2.000  lb.     2.200  Ib.     2.400  Ib.     2,600  Ib. 

Cubic  feet  air  per  pound  pig.  .      44.2  49.1  54.0  58.9  63.8 

Moisture  in  Blast — The  decomposition  of  the  moisture  in 
the  furnace  hearth  absorbs  heat  according  to  the  quantity  pres- 
ent. Except  for  occasional  leaks  in  water  coolers,  the  only  source 
of  moisture  in  the  hearth  is  that  contained  in  the  blast  of  air. 
The  quantity  of  moisture  in  the  air  at  any  moment  depends  upon 
its  temperature  and  the  degree  of  humidity.  According  to  the 
records  of  the  United  States  Weather  Bureau,  the  average  tem- 
perature and  humidity  at  Philadelphia,  Pa.,  from  1874  to  1904 
was  as  follows: 

Temperature.     Humidity. 
Degrees  F.         Per  cent. 

Spring  months 51  67 

Summer    months 74  70 

Fall  months 57  73 

Winter  months 34  74 

Assuming  an  average  for  the  State  of  Pennsylvania  of  S7 
degrees  F.  temperature  and  70  per  cent,  humidity,  we  have,  from 
Davis's  Meteorology,  p.  143,  that  there  are  approximately  5.3 
grains  of  water  in  each  cubic  foot  of  saturated  air  at  57  degrees 
F.,  of  which  70  per  cent,  amounts  to  about  3.7  grains.  The  quan- 
tity of  water  in  the  air  that  is  needed  to  consume  the  fuel  which 
is  required  to  smelt  100  pounds  of  pig  iron  may  be  found  as 
follows : 

no.  cu!  ft.   X  grs.  per  cu.  ft.  __  5300  X   37   __   28l    lbs     av 

grs.  per  lb.  av.  7000 

By  the  reaction,  H2O  +  C  =  CO  +  H2,  it  appears  that  for 
18  pounds  of  water  in  the  form  of  steam  which  is  decomposed, 
12  pounds  of  carbon  are  oxidized  to  the  condition  of  CO.  One 
pound,  H2,  burned  to  the  condition  of  steam,  gives  51,750  B.  T. 

U.     For  each  pound  of  steam,  the  heat  given  off  will  be  -- 

=  5750  B.  T.  U.,  which  will  be  absorbed  on  decomposition.    The 
heat  given  off  by  the  corresponding  quantity  of  carbon,  burned 


Action  Within  the  Furnace.  213 

to  CO  is  4450  X-^|-~  2965  B.  T.  U.     5750  —  2965  ==  2785  B. 

T.  U.,  which  is  the  net  amount  of  heat  absorbed  per  pound  steam ; 
2785  X  2.81  —  7826  B.  T.  U.,  which  is  absorbed  in  decomposing 
the  moisture  in  the  blast  for  each  100  pounds  of  pig  made.  This 

amount   of   heat   is   equivalent   to  •?—     =    1.76   pounds   carbon 

4450 

burned  at  the  tuyeres,  which  equals  2%  pounds  coke  of  78  per 
cent,  efficiency,  or  50  pounds  coke  per  ton  of  pig. 

The  saving  of  such  a  small  amount  of  fuel  hardly  appears  to 
be  a  sufficient  incentive  to  efforts  to  desiccate  the  blast.  Never- 
theless this  was  successfully  accomplished  with  great  profit  by 
Gayley,  who  cooled  his  blast  by  means  of  refrigeration  from  71  , 

A  r.  A.  1.  M.  E., 

degrees  F.  to  25  degrees  F.,  thereby  reducing  the  moisture  from  xxxv.)P.  746. 
5.66  to  1.75  grains  per  cubic  foot.     The  removal  of  3.91  grains 
per  cubic  foot  is  equivalent  to  about  63  pounds  per  ton  of  iron. 

— —^  —  39.4  pounds  carbon,  or  50.5  pounds  coke  per  ton 

445° 

of  pig.  Yet  the  observed  economy  was  far  greater  than  expected. 
The  fuel  consumption  per  ton  of  pig  dropped  from  2147  to  1726 
pounds,  and  the  daily  output  rose  from  358  to  447  tons  of  pig. 
The  cumulative  benefits  of  the  reduction  of  fuel  were  very  mani- 
fest. The  blast  requirements  fell  from  40,000  to  34,000  cubic 
feet  per  minute,  with  a  consequent  rise  in  temperature  of  720 
to  870  degrees  F.,  the  temperature  of  the  escaping  gases  fell 
from  538  to  376  degrees  F.,  and  they  were  of  considerably  less 
volume,  thereby  carrying  away  less  heat.  The  carbon  ratio  also 
fell  from  1.71  to  1.24.  The  summary  below  shows  the  change 
very  clea  rly.  1 6  days  dry  blagt> 

11  days  natural  blast,  August  25-Sep- 

August  1-11  inclusive,  tember  9  inclusive. 

Average   moisture 5.66  grs.  per  cu.  ft.  1.75  grs.  per  cu.  ft. 

Average  daily  output 358  tons.  447  tons. 

Average    fuel    consumption 2,147  pounds.  1,726  pounds. 

Average  ore  per  unit  of  fuel.  . 1.96  2.35 

Number  revolutions  engine 114  per  minute.  96  per  minute. 

Cubic  feet  air 40,000  per  minute.  34,000  per  minute. 

Temperature  of  blast 720  degrees  F.  870  degrees  F. 

CO  in  gases 22.3  per  cent.  19.9  per  cent. 

CO2  in  gases 13.0  per  cent.  16.0  per  cent. 

Temperature  of  gases 538  degrees  F.  376  degrees  F. 

Flue  dust 5.0  per  cent.  1.0  per  cent. 

Indicated   horse-power 2,700  2,013 

Indicated  horse-power  per  ton  coke 7.87  5.84 


214  Blast  Furnace. 

The  credit  for  the  most  satisfactory  explanation  of  this  re- 
markable result  belongs  to  J.  E.  Johnson,  Jr.,  who  points  out 
that  for  every  operation  of  smelting  a  certain  critical  tempera- 
ture is  necessary  to  perform  the  essential  operations  of  the  proc- 
ess, such  as  the  reduction  of  the  iron  and  metalloids,  the  fusion 
and  superheating  of  the  metal,  the  formation,  fusion  and  super-- 

Tr'Axxxv^!  heating  of  the  slag,  etc.  This  critical  temperature  corresponds 
closely  to  the  melting  point  of  the  slag  and  varies  with  its  basicity. 
The  theoretical  minimum  quantity  of  heat  needed  by  the  furnace 
is  the  heat  that  will  raise  the  products  of  combustion  and  contents 
of  the  hearth  to  the  critical  temperature,  and  it  is  only  the  excess 
above  this  point  that  is  available  for  meeting  contingencies,  such 
as  decomposition  of  water,  etc.  Any  reduction  in  the  extra  heat 
requirements,  as  in  decreasing  the  quantity  of  moisture,  leaves 
an  excess  of  heat  above  that  required  by  the  critical  temperature, 
which  permits  of  a  corresponding  decrease  of  fuel. 

It  has  been  pointed  out    by   many,   that    the    great    saving 

Tr.  A.  i.  M.  E.,    resulting  from  the  drying  of  the  blast  is  due    to    the    increased 

XXXVII 

V  38.5!  regularity  of  working,  in  consequence  of  which  it  is  not  necessary 
to  carry  an  excess  quantity  of  fuel  when  the  atmosphere  is  dry,  in 
order  to  have  a  sufficiency  to  meet  the  emergencies  caused  by 
varying  degrees  of  humidity.  As  calculated  by  Richards,  the 
saving  of  the  20  per  cent,  of  fuel  per  100  pounds  of  pig,  is  dis- 
tributed as  follows: 

Per  cent. 

Less  moisture  to  decompose , -2.95 

Less  wasted  in  gases 5.25 

Less    radiation 3.70 

Less  carbon  ratio 6.90 

Less  heat  in  slag 0.10 

Less  heat  in  blast 0.40 

Total 19.30 

If  the  moisture  could  be  held  constant  at  any  point,  and  the 
above  equivalent  of  heat  introduced  in  any  form,  such  as  increased 
blast  temperature,  it  is  evident  that  the  same  fuel  saving  could  be 
effected  with  its  attendant  advantages. 

The  air  for  the  blast  is  usually  drawn  from  the  engine  room, 
and  is  therefore  nearly  saturated  with  moisture.  The  outside 
air  rarely  averages  over  70  per  cent,  of  saturation,  and  frequently 
gets  down  to  50  per  cent.  It  is  therefore  desirable  to  draw  the 


Action  Within  the  Furnace. 


215 


supply  directly  from  out  of  doors.  Even  very  moderate  cooling 
of  air  has  a  considerable  effect  upon  the  quantity  of  moisture 
present. 

1  cubic  foot  saturated  air  at  90  degrees  F.  contains  15  grs.  vapor. 

1  cubic  foot  saturated  air  at  70  degrees  F.  contains  8  grs.  vapor. 

1  cubic  foot  saturated  air  at  50  degrees  F.  contains  4  grs.  vapor. 

1  cubic  foot  saturated  air  at  30  degrees  F.  contains  2  grs.  vapor. 

For  each  drop  of  20  degrees  F.,  the  saturation  point  is  halved. 
Moreover,  since  the  amount  of  vapor  that  can  exist  in  a  given 


100 

w 

^ 

7 

\ 

\ 

CO 

z 
o 

no  m  n 

2 

£ 

f  Sl 

y 

\ 

\ 

h 

z 

CD 

^ 

^^ 

2 

j 

\ 

} 

s\ 

^x 

90  o 

Q. 

80    £     8 

\> 

r 

1 

\/ 

\ 

U. 

O 

Q 

/ 

'      \ 

Ste 

g 

I 

\^ 

z 
o 

<U      5       t 

3 

^1 

^ 

^ 

L 

\ 

- 

80   5 

U. 

TO      °       r 

^ 

N 

\o 

/ 

' 

L 

2 

00     ui      5 

_J 

1 

/ 

o. 

U. 

0  i  4 

30           3 

I 

\ 

7 

\ 

/ 

_ 

70   3 

°fl              2 

/ 

'  ^ 

/ 

i 

^^ 

7 

f)             0 

/ 

uj 

*N.     FE 

B.        Mf 

R.      AF 

R.        M 

\Y       JU 

NE       JU 

LY      AU 

G.     SE( 

ST.      OC 

T.      NC 

V.       DE 

C. 

Diagram  Illustrating  the  Relation  Between  Moisture  in  the  Air  Upon  Fuel 
Consumption   and   Output. 

space  is  dependent  upon  the  temperature  and  independent  of  the 
presence  of  other  gases,  it  follows  that  when  at  15  pounds  pres- 
sure 2  cubic  feet  of  air  are  compressed  into  i  cubic  foot  of  space 
without  change  of  temperature,  there  can  be  only  one-half  as 
much  moisture  to  each  pound  of  air.  From  these  considerations,  iron  Age, 

....  Mch.  22,  1906, 

it  is  evident  that  even  very  moderate  but  uniform  temperatures  of   P-  1032. 
air  may  work  decided  benefit  in  promoting  regularity  of  working, 
through  simple  water  cooling,  and  without  expensive  apparatus. 
The  accompanying  diagram  illustrates  the  effect  of  increased 


216  Blast  Furnace. 

moisture  in  the  air  upon  the  fuel  consumption  and  output  of  a 
blast  furnace. 

Volume  of  Gases  —  When  the  blast  comes  into  contact  with  the 
coke  in  the  hearth  of  the  furnace  it  burns  to  the  condition  of  CO 
mixed  with  the  residual  nitrogen  and  hydrogen,  whose  volume, 
under  atmospheric  pressure  at  60  degrees  F.  may  be  calculated  as 
follows  : 

Cubic  feet. 
CO,  1G0.56  X  13.5  -   ................................  2,280 

N,  310.55  X  13.5  =   .................................  4,192 

H,  0.31  X  189.7  -   ..................................       59 

Total  ..........................................  6,540 

At  the  temperature  of  3500  degrees  F.  the  volume  of  these  gases, 
if  unconfmed  would  be  increased,  as, 

458-5^     6  t.         Qr 


60  +  458.5 
•—  X  7-6  ==.  9.4  times  the  volume  of  the  original  blast.     Under 

furnace  pressure,  however,  this  volume  is  probably  diminished  by 
nearly  one-half. 

The  volume  of  the  waste  gases  as  compared  with  the  blast 
may  be  found  as  follows  : 

Cu.  ft. 
C02   .  .  .  .....................  106.40  X       8.6  =  ........................     915 

CO    .........................  136.16  X    13.5  —  ........................  1,838 

N2    .........................  31  0.55  X    13.5  ==  ........................  4,192 

II2   .........................      0.31  X  189.7  =  .....................  ...       58 

HjO    .  .    17.75  X    26.3  ~  .  .  .     467 


Totals 571.17  7,470 

which  shows  that  the  volume  at  the  same  temperature  and  pres- 
sure, as  well  as  the  weight,  has  increased  to  a  little  more  than  1.4 
times  that  of  the  blast.  At  the  temperature  of  escape,  however, 
the  volume  is  in  the  ratio  of  their  absolute  temperatures,  or 

-~-  X  1.41=2.5  times   the    volume  of   the    original    blast   at 
5l°-5 
atmospheric  temperature  and  pressure. 

Latent  Heat  of  Expansion  of  Gases The  expansion  of  the 

gases  due  to  the  sudden  rise  of  temperature  from  1200  degrees 
F.  to  3500  degrees  F.  renders  latent  a  considerable  quantity  of  the 


Action   Within  the  Furnace.  217 

heat  developed  in  the  hearth.  If  the  gases  were  allowed  to  expand 
freely  under  atmospheric  pressure  in  proportion  to  the  increase 
of  temperature,  we  would  expect  them  to  render  latent  a  quantity 
of  heat  as  follows  : 

B.T.  U. 

CO,  169.56  X  2,300  X  0.0715  — 27,884 

N2,  310.55  X  2,300  X  0.0715  = 51,070 

H2,  0.31  X  2,300  X  0.095  =  711 


Total . 


which  is  equivalent  to  about  20  pounds  of  coke  burned  at  the 
tuyeres  per  100  pounds  of  pig.  However,  as  the  pressure  existing 
in  the  hearth  prevents  free  expansion,  the  heat  rendered  latent 
by  expansion  up  to  the  bosh  probably  does  not  greatly  exceed  half 
that  amount.  A  large  proportion  of  the  latent  heat  is  returned 
to  the  materials  through  the  cooling  and  consequent  contraction 
of  the  gases  as  they  pass  upward  through  the  furnace.  The  latent 
heat  of  expansion  above  60  degrees  which  is  held  by  the  gases  as 
they  escape  from  the  furnace  at  450  degrees  F.  may  be  determined 
as  follows : 

B.  T.  U. 

C02,  106.40  X  390  X  0.0455  - 1,888 

CO,  136.16  X  390  X  0.0715  =  . . . 3,797 

N2,  310.55  X  390  X  0.0715  = 8,660 

H2,  0.31  X  390  X  0.995  = 120 


Total 14,465 

which  is  equivalent  to  about  4  pounds  of  coke  burned  at  the 
tuyeres,  per  100  pounds  of  pig.  It  is  evident,  therefore,  that  the 
latent  heat  rendered  sensible  again  through  the  contraction  of  the 
gases  during  their  passage  through  the  furnace,  returns  to  the 
stock  all  except  this  quantity  of  the  heat  originally  rendered  latent 
through  expansion  of  gases  in  the  hearth. 

Latent  Heat  of  Expansion  of  Blast — The  heat  rendered 
latent  by  the  expansion  of  the  blast  through  its  rise  in  tempera- 
ture from  60  to  1 200  degrees  F.  during  its  passage  through  the 
stoves  would  amount  to 

4°775  +  1140  X  0.069  =  32,070  B.  T.  U. 
if  the  blast  expanded  freely  under  atmospheric  pressure.     Since 
the  blast  is  under    upwards    of    two    atmospheres    pressure,  the 
amount  of  expansion  is  about  halved  and  the  latent  heat  of  expan- 


218  Blast  Furnace. 

sion  of  the  incoming  blast  is,  in  consequence,  probably  about 
16,000  B.  T.  U.  \Ye  have  seen  that  the  latent  heat  of  expansion 
lost  in  the  escaping  gases  is  something  under  15,000  B.  T.  U.  It 
is  probable,  therefore,  that  there  is  no  net  loss  of  heat  to  the 
furnace  through  heat  rendered  latent  by  expansion  of  gases,  but, 
on  the  contrary,  a  slight  gain.  This  gain,  however,  is  more  than 
neutralized  by  the  heat  rendered  latent  in  vaporizing  and  expand- 
ing- the  moisture  of  the  charge,  thus: 

B.T.U. 

absorbed. 

Water  60°  —  Steam  =  17.75  X  1,118  B.  T.  U  = 19,845 

Steam  212°  —  450°  =  17.75  (238°  X  0.42  +  238°   X  0.000185)   = 1,775 


Tota! 21,620 

This  absorption  of  heat  is  very  efficient  in  keeping  down  the  tem- 
perature of  the  furnace  top. 

REDUCTION  OF  METALLOIDS. 

We  have  seen  that  the  iron  is  easily  reduced  by  gaseous  carbon 
in  the  form  of  CO,  and  that  its  reduction  is  largely  accomplished 
very  early  in  the  process.  The  metalloids  which  combine  with 
the  iron  to  form  the  pig  are  not  so  easily  affected,  however,  and 
consequently  do  not  relinquish  their  original  combinations  until 
they  are  subjected  to  very  strong  persuasion  at  a  considerable 
depth  in  the  furnace. 

Manganese — The  most  readily  reduced  of  the  metalloids  is 
probably  manganese.  It  is  usually  present  in  the  ore  as  dioxide, 
MnO2,  and  it  is.  probable  that  it  is  never  completely  reduced  in 
the  blast  furnace.  Under  ordinary  conditions,  about  two-thirds 
of  the  manganese  in  a  pig  iron  mixture  is  reduced  to  the  metallic 
condition  and  enters  the  iron,  while  the  remaining  third  enters 
the  slag  and  combines  with  SiO2  in  the  form  of  MnO.  Since  its 
entrance  into  the  slag  is  opposed  by  a  slag  of  increased  basicity, 
highly  calcareous  slags  tend  to  drive  the  manganese  into  the 
iron.  This  disposition  is  favored,  also,  by  high  temperatures  and 
strongly  reducing  conditions. 

Silicon — The  silicon  which  enters  pig  iron  is  derived  from 
the  silica  which  is  invariably  present  as  gangue  of  the  ores,  im- 
purity in  the  fluxes,  and  ash  of  the  fuels.  The  quantity  of  silicon 
which  enters  pig  iron  usually  ranges  from  I  to  3  pounds  per  100 


Action  Within  the  Furnace.  219 

pounds  pig,  while  the  quantity  entering  the  slag  may  range  from  5 
to  15  pounds,  but  is  usually  about  7  pounds.  Silica  is  not  at  all 
affected  by  CO  and  probably  is  not  decomposed  by  solid  carbon  or 
other  reagent  even  at  the  highest  furnace  temperature,  except  in 
the  presence  of  a  metallic  matrix  with  which  the  silicon  can  unite 
at  once,  forming  a  silicide.  The  element  is  highly  oxidizable  and 
needs  to  form  a  protecting  union  immediately  in  order  to  preserve 
its  elemental  condition.  The  reaction  evolves  CO,  and  may  be 
represented  thus : 

SiO2  +  2C  =  Si  +  2CO. 

At  temperatures  below  2700  degrees  F.,  silicon  will  absorb  oxygen 
at  the  expense  of  the  oxides  of  carbon,  and  it  is  only  at  tempera- 
tures well  above  this  that  the  preferential  relation  is  reversed  and 
reduction  of  silicon  by  carbon  becomes  possible.  It  is  evident 
then,  that  reduction  of  silicon  can  take  place  only  within  the 
melting  zone.  We  have  seen  already  that  the  silica  of  the  gangue 
and  flux  are  melted  at  temperatures  about  3000  degrees  F.,  and 
having  once  entered  the  slag,  the  silicon  is  probably  secure  from 
reduction.  It  is  highly  probable,  therefore,  that  the  bulk  of  the 
silicon  is  derived  from  the  only  remaining  source,  namely  the  ash 
of  the  fuel.  This  probability  is  well  substantiated  by  the  fact  that 
siliceous  fuels  always  produce  higher  silicon  iron  than  when 
the  silica  of  the  charge  exists  mainly  in  the  gangue  of  the  ore. 

The  reaction,  SiO2  +  2C.=  Si  +  2CO,  represents  a  consider- 
able absorption  of  heat,  thus  : 

B.T.TJ. 

Heat  absorbed  in  reducing  1  pound  Si  — 11,571.5 

24 
Heat  given  out  by  corresponding  amount  of  carbon,  —  X  4,450  = 3,814.5 


Net  heat  absorbed  per  pound  Si  — 7,757.0 

7757  X  1.5  =  1 1,635  'B.  T.  U.  absorbed  by  the  reaction,  per 
TOO  pounds  pig. 

Phosphorus. — Phosphorus  enters  the  furnace  in  all  members 
of  the  charge.  It  is  usually  in  the  form  of  calcic  phosphate,  called 
apatite,  Ca3P2O8.  This  compound  is  not  affected  by  CO,  and  is 
probably  not  dissociated  by  heat  alone,  in  any  part  of  the  furnace. 
In  the  presence  of  silica,  at  slag-forming  temperatures,  however, 
it  can  release  its  CaO  to  the  slag,  leaving  the  P2O5  free  for  reduc- 


220  Blast  Furnace. 

tion.  As  the  reduction  of  phosphorus  from  its  oxide  is  difficult, 
it  is  probably  accomplished  by  solid  carbon,  thus : 

P.O.  +  5C  ==  P2  +  SCO. 

For  ordinary  charges  and  furnace  conditions,  this  reaction  is  com- 
plete, and  practically  all  of  the  phosphorus  in  the  charge  enters 
the  iron.  Exceptional  conditions,  such  as  a  very  highly  phos- 
phoric charge,  or  a  highly  basic  or  ferruginous  slag,  may  result  in 
some  elimination  of  phosphorus,  but  it  is  safe  to  assume  that 
ordinarily  all  of  the  phosphorus  charged  in  ore,  fuel  and  flux 
will  enter  the  iron.  The  reduction  of  phosphorus  is  an  endo- 

thermic  reaction  also,  as  shown  thus : 

B.  T.  u. 

float  absorbed  in  reduction  of  1  pound  P  ™ 10,GOr>  n 

60 
Heat  generated  by  equivalent  amount  of  carbon,  —  X  4,450  =: 4,306.4 


Net  beat  absorbed  per  pound  1*  — 6,Li99.2 

6299.2  X  0.5  =  3149.6  B.  T.  U.,  absorbed  by  reaction  per  100 
pounds  pig. 

Sulphur — Sulphur  enters  the  furnace  in  a  variety  of  ways. 
It  may  be  present  in  the  form  of  either  sulphate  or  sulphide  in 
each  member  of  the  charge,  but  usually  at  least  90  per  cent,  of 
that  present  is  found  in  the  fuel.  It  exists  in  coke  in  three 
different  conditions :  a  small  portion  as  sulphide  can  be  evolved  as 
H2S,  a  small  portion  can  be  separated  as  sulphate  of  metals,  and 
the  remainder,  ranging  from  65  to  90  per  cent.,  exists  in  combina- 
tion with  the  carbon.  Ordinarily  the  quantity  of  sulphur  in  the 
charge  does  not  vary  much  from  I  pound  for  every  100  pounds 
of  pig  made,  and  of  this  quantity  2  to  10  per  cent,  usually  finds  its 
way  into  the  iron.  The  bulk  of  the  remainder  enters  the  slag, 
while  a  small  percentage  is  volatilized. 

Since  most  of  the  sulphur  is  held  by  the  carbon,  it  follows 

that  it  is  not  released  until  the  carbon  is  burned  before  the  tuyeres. 

The  greater  part  is  burned  to  SO2,  but  about  15  per  cent,  escapes 

as  SO3.     Its  volatility  was  found  by  Wuest  and  Wolff  to  differ 

Insi906Ui''    with  tne  temperature,  and  the  nature  of  the  atmosphere.     The 

406-    evolution  is  most  nearly  complete  in  the  presence  of  hydrogen  or 

steam,  less  complete  with,  CO  and  CO2,  and  least  satisfactory  with 

nitrogen.    The  action  in  any  atmosphere  is  accelerated  by  higher 

temperatures. 


Action  Within  the  Furnace. 


221 


Per  cent,  sulphur  present  volatilized  in  the  presence  of 


930  degrees  F  

H2. 
7.59 

Steam. 
12.84 

N2. 
2.41 

CO. 

12.80 

CO,. 
6.47 

1  110  degrees  F  

22.99 

13.27 

4.90 

16.89 

8.32 

1,470  degrees  F  
1,650  degrees  F  
1,830  degrees  F.  .  

41.87 
45.77 
51.17 

36.8'? 
51.52 
54.34 

5.90 
6.97 
17.35 

30.80 
37.61 
38.32 

16.00 
25.46 
59.24 

By  passing  a  mixture  of  the  above    gases    of   the    following 
proportions : 


56.0 


CO. 

28 


CO2< 
13.5 


H2 
2.5 


over  Fe2O3,   CaCCX   and  a  mixture   of  the  two,   the   following 
comparative  results  were  obtained : 


Per  cent,  of  total  sulphur 
which  was  volatilized. 


480 

degrees 

F.  .  . 

.  .  .44.32° 

CaCO3: 
61.74 

CaC03. 
41.51 

930 

degrees 

F.  .  . 

.  .  .49.31 

59.94 

33  31 

1  110 

degrees 

F 

.  .    47  17 

53  47 

31  17 

1  470 

degrees 

F 

58  67 

42  66 

40  49 

1  650 

F 

58  39 

40  91 

51  27 

1.830 

decrees 

F.. 

..53.64 

40.57 

34.47 

62.66 


CaCO3. 

10.26 

16.68 

47.05 

68.08 

85.74 

91.83 


Fe2O3.  CaCO3. 


Per  cent,  of  volatilized  sulphur 
which  was  absorbed. 

Fe2O3+  CaCO3 
Fe2O3 
53.06 
64.02 
68.33 
69.58 
68.02 


56.51 
59.44 
59.32 
18.28 
41.03 
0.0 


0 

0 

2.34 
45.78 
43.00 
100.64 


At  low  temperatures,  Fe2O3  absorbs  sulphur  and  is  partially 
reduced  by  it.  At  low  temperatures,  CaCO3  is  not  active  in 
absorbing  sulphur.  At  noo  degrees  F.,  however,  CaCO3  becomes 
more  active  and  at  1800  degrees  F.,  the  absorption  is  practically 
complete.  This  is  because  CaCO3  begins  to  decompose  at  noo 
degrees  F.  The  action  is  not  strong,  however,  until  the  tempera- 
ture approaches  1500  degrees  F.,  when  it  begins  to  cohere.  At 
1650  degrees  the  reaction  becomes  violent  and  at  1800  degrees  it 
is  practically  complete.  It  appears,  then,  that  sulphur  does  not 
reach  the  hearth  in  its  original  condition,  but  is  volatilized  and 
passes  up\vard  to  be  absorbed  by  members  of  the  charge  and 
brought  back  to  the  melting-zone  again.  At  temperatures  below 
noo  degrees  F.,  it  is  absorbed  chiefly  by  Fe2O3,  but  at  tempera- 
tures above  1650  degrees  F.,  the  bulk  is  absorbed  by  the  CaCO3. 

Since  sulphur  is  an  acid  radical,  whether  it  is  in  the  oxidized 
or  elemental  condition,  it  combines  readily  with  bases  of  the  slag, 
such  as  lime,  and  the  more  basic  the  slag,  the  more  strongly  it 
will  be  held.  Under  ordinary  conditions,  it  unites  with  lime  to 
form  a  sulphide  of  calcium,  which  is  dissolved  in  the  slag. 


222  Blast  Furnace. 

It  is  the  universal  experience  that  sulphur  is  best  excluded 
from  pig  iron  in  the  presence  of  a  basic  cinder  at  high  tempera- 
tures. This  fact  may  be  accounted  for  in  several  ways.  It  was 
formerly  considered  that  the  high  temperature  volatilized  the 
sulphur^  but  owing  to  condensation  in  cooler  parts  near  the 
top  of  the  furnace,  more  or  less  of  the  sulphur  is  returned 
to  the  hearth,  therefore  this  theory  does  not  hold.  It  has 
Tour  \m  keen  snown  recently  that  sulphur  forms  with  silicon  a  sub- 
iuf Jfsu.'  sulphide  that  is  volatile,  which  may  account  for  its  elimination 
from  hot  furnaces  where  much  silicon  is  reduced.  High  silicon 
irons  are  generally  noticeably  free  from  sulphur,  and  this  fact 
has  been  attributed  to  their  incompatibility.  But  it  is  more  likely 
that  the  reduction  of  silicon  leaves  the  slag  more  basic  and  hence 
better  able  to  retain  sulphur.  In  the  presence  of  metallic  man- 
ganese, sulphur  unites  to  form  a  stable  sulphide  which  enters  the 
slag,  leaving  the  iron  comparatively  free  from  sulphur. 

CYANIDES. 

The  action  of  the  nitrogen  of  the  blast  'upon  the  hot  carbon 
in  the  hearth  results  in  the  formation  of  small  quantities  of 
cyanogen,  CN.  Cyanogen  shows  a  decided  affinity  for  the  sodium 
and  potassium  which  are  usually  present  in  small  quantities  in  the 
nst  jour  ^ue^  asn>  anc^  as  a  result,  cyanides  of  the  alkali  metals  are  found 
1S8i;''jgr:'  in  the  gases  in  all  parts  of  the  furnace.  Bell  found  that  the 
average  quantity  in  a  coke  furnace  for  six  consecutive  days  was 
6.58  grains  of  cyanogen  per  cubic  feet  of  gases  in  the  hearth,  and 
1.65  at  the  top,  or  about  130  and  33  pounds  respectively  per  ton 
pig,  which  would  indicate  at  least  double  these  quantities  of  the 
mixed  sodic  and  potassic  cyanides.  The  action  of  the  cyanides 
upon  the  members  of  the  charge  is  not  well  understood.  It  is 
known,  however,  that  they  are  strong  reducing  agents,  since  they 
take  up  oxygen  and  form  cyanates.  Experiments  by  Bell  show 
that  they  are  more  active  than  CO  in  the  presence  of  CO2,  thus : 

Tern-  . —  —Per  100  parts  iron  present. — 

, — Gas  mixture.— >>        perature,  Time,  Carbon 

Vol.  CN.  Vol.  CO2.       degrees  1?.  hours.        Fe  as  metal.  Fe  as  oxide.       deposited. 
Ibid,          1                     6                   1,288  2%  56.3  43.7  28.50 

p-556>         1  15  1,482  2%  6.5  93.4.  1.30 

1  30  1,427  3  0.9  99.1  2.52 


Action  Within  the  Furnace:.  223 

This  shows  that  cyanides  are  very  active,  even  when  CO2  is  six 
times  their  volume,  which  would  quite  neutralize  CO. 

For  this  reason  some  metallurgists  attribute  great  importance 
to  the  cyanides  as  reducing  agents.  Their  action  may  be  repre- 
sented by  the  following  equation, 

KCN  +  FeO  =  Fe  +  KCNO. 

The  resulting  potassic  cyanate  passes  upward  in  the  current  of 
gases  and  is  probably  decomposed  by  CO2  into  carbonates  with 
the  liberation  of  the  nitrogen,  thus: 

2KCNO  +  CO2  =  K2CO3  +  CO  +  N2,  or 
KCN  +  KCNO  +  CO2  =  K2  CO3  +  2CN. 

The  potassic  carbonate  is  undoubtedly  deposited  in  the  cooler 
parts  of  the  furnace  and  carried  downward  by  the  descending 
materials  to  the  hearth,  where  it  can  again  act  as  a  base  for 
cyanogen.  In  this  way,  the  quantity  of  cyanides,  which  depend 
for  existence  upon  the  presence  of  alkalis,  is  cumulative,  and  is 
said  to  amount  sometimes  to  as  much  as  2  cwts.  of  cyanogen  per 
ton  of  iron.  The  removal  of  the  last  traces  of  oxygen  from'  the 
ore  in  the  descending  charge  is  credited  by  some  to  the  action  i 
of  cyanides  instead  of  to  the  deposited  carbon.  The  fact  that 
reduced,  spongy  iron  shows  little  or  no  carbon  when  it  reaches 
the  melting  zone,  lends  color  to  this  theory.  However,  130 
pQunds  per  ton  is  equivalent  to  5.8  pounds  CN  per  100  pounds 
pig,  and  is  capable  of  removing  3.55  pounds  of  oxygen  from  the 
ore,  which  is  only  about  80  per  cent,  of  that  usually  removed  by 
.solid  reagents.  It  is  probable,  therefore,  that  the  reduction  is 
completed  by  the  joint  action  of  carbon  and  cyanides.  The 
gradual  accumulation  of  cyanides  in  a  blast  furnace. may  partially 
account  for  the  continuous  improvement  in  its  action  during  the 
first  few  months  of  a  blast. 

A  considerable  quantity  of  cyanides  escape  from  the  furnace 
in  fume  and  flue-dust,  and  owing  to  their  extremely  poisonous 
character  should  be  handled  carefully.  In  1901,  20  tons  of  flue- 

Inst.  Jour. 

dust,  deposited  in  the  River  Ems  in  Styria,  caused  the  death  of  a 
great  number  of  fishes,  for  which  the  furnace  company  was  fined 
$14,000.  In  1898,  a  similar  accident  happened  in  the  Rockaway 
River  at  Wharton,  New  Jersey. 


224  Blast  Furnace. 

ANOMALIES    IN    GAS    COMPOSITION. 

The  refixing  in  the  form  of  cyanides  and  carbonates  of  the 
carbon,  which  has  been  gasified  at  the  tuyeres  causes  a  tem- 
porary withdrawal  of  both  C  and  O  from  the  gases  in  the  middle 
of  the  furnace:  Numerous  analyses  of  the  gases  by  Bell  gave 
this  general  result : 

Place  of  sample.                                                                  C.  O.  O  expected. 

Inst.  Jour.,    Hearth 20.43  27.74  27.24 

188 Vsi'    J«st  above  bosh 18.25  26.01  26.28 

Top 20.96  33.40  36.15 

It  may  be  observed  that  the  quantity  of  oxygen  in  the  hearth 
is  slightly  in  excess  of  the  nitrogen  as  well  as  of  the  carbon.  This 
is  due  to  the  fact  that  some  of  the  oxygen "  comes  from  the 
moisture  in  the  blast  and  from  the  reduction  of  metalloids  while 
some  of  the  nitrogen  is  withdrawn  to  form  cyanides.  By  the 
time  the  gases  have  reached  the  bosh,  they  show  a  distinct  deficit 
of  both  carbon  and  oxygen,  that  of  .  the  latter  being  somewhat 
more  pronounced.  This  is  no  doubt  due  to  the  fact  that  the 
atomic  equivalent  of  oxygen  in  cyanates  and  carbonates  is  greater 
than  that  of  carbon.  It  is  unsafe  to  speculate,  however,  on  the 
conditions  of  equilibrium,  since,  as  we  have  already  seen,  both 
carbon  and  oxygen  are  deposited  from  the  gases  through  the 
influence  of  the  reduced  iron  sponge.  That  the  carbon,  oxygen, 
and  nitrogen  are  more  or  less  perfectly  restored  to  the  gas  current, 
is  accounted  for  by  the  decomposition  of  the  alkaline  cyanates  and 
carbonates  in  the  upper  part  of  the  furnace.  The  imperfections 
of  the  restoration  may  be  at  least  partly  explained  by  the  fact  that 
solid  matter  is  carried  out  of  the  furnace  in  the  "  fume,"  which 
is  borne  away  by  the  current  of  gases. 

Fume — The  fume  is  the  finely  divided  particles  of  solid 
matter  which  float  in  the  gaseous  current,  giving  it  its  charac- 
teristic whitish  appearance  as  it  issues  from  the  furnace  and 
chimneys.  The  appearance  of  the  fume  varies  with  the  quantity 
of  matter  carried,  being  white  and  dense  when  the  furnace  is  hot, 
and  thin  and  bluish  when  the  furnace  is  cold.  It  is  therefore  an 
indication  of  the  internal  condition  of  the  furnace.  Some  of  the 
material  which  exists  in  the  gases  in  the  hotter  parts  of  the 


Action  Within  the-  Furnace. 


225 


furnace  is  condensed  before  the  gases  escape  and  hence  docs  not 
appear  in  the  fume,  while  other  material  is  caught  up  early  in 
the  descent  by  the  current  and  so  never  reaches  the  lower  part 
of  the  furnace.  The  former  diminishes  as  the  gases  pass  upward, 
while  the  latter  increases.  The  following  analyses,  selected  from 
those  of  Bell,  at  Clarence,  England,  illustrate  the  changeableness 
of  composition  of  the  solid  constituents  of  the  gases  while  in  the 
furnace : 


Distance  above   tuyeres. 

.  ,      2  ft. 

261/2  ft. 

39%  ft. 

451/2  ft. 

5814  ft. 

76ft. 

Probable  temperature.  .  .  . 

.3,500°  F. 

2,000°  F. 

1,800°  F. 

1,600°  F. 

900°  F. 

600°  F. 

Grs.    fume   per    cubic   fo 

ot 

gases    

.  .      5.95 

3.38 

0.99 

0.61 

0.72 

0.83 

KCN  

.  .    75.98 

89.20 

71.21 

NaCN  

3.51 

0.07 

.  . 

.  .  . 

K2CO3    .  .  ;  

.  .      3.95 

^2  21 

Na2CO3    

.  .    20.70 

3.52 

3.91 

r 

NH4C1    



2.33 

KC1    

.  .      0.55 

5.42 

1.80 

5.92 

NaCl    

2.48 

6.20 

2.93 

1.00 

1.48 

ZnO    

.  .      Tr 

Tr. 

6.71 

15.27 

17.17 

13.39 

PbCl2    

1.47 

8.77 

Bell's 
"Principles"  of 

CaSO4    

... 

Tr. 

0.57 

3  «0     Manufacture  of 
1     Iron  and  Steel, 

feiO,  

6.38 

15.00 

10.25     p.  225. 

CaO   

6.70 

14.37 

0.56 

A12O3    

.  .  . 

... 

1.84 

6.11 

3.66 

MgO   

0.31 

4.33 

Tr. 

FeO    

.  .  . 

... 

1.03   ' 

2.63 

.  .  . 

Fe203  

15.00 

c  

0  27 

0  41 

13  66 

Composition  of  gases. 

C02  

..      1.90 

0.46 

0.00 

3.84 

6.56 

10.69 

CO    

..  .39.18 

35.80 

34.82 

32.33 

32.25 

28.58 

H2   

.  .      1.97  - 

1.14 

1.41 

3.88 

1.08 

1.70 

N2  

.  .    56.95 

62.60 

63.77 

59.95 

60.11 

59.03 

REDUCTION    BY    CHARCOAL. 

The  process  of  reduction  of  iron  ore  in  a  charcoal  furnace 
appears  to  be  of  a  nature  somewhat  different  from  that  in  a  coke 
furnace.  Whereas,  in  coke  furnaces  reduction  begins  almost  as 
soon  as  the  ore  is  charged  and  is  practically  complete  at  a  depth 
of  20  feet,  in  charcoal  furnaces,  which  are  usually  of  much  less 
height,  the  reduction  has  hardly  begun  at  that  depth.  A  com- 
parison of  the  composition  of  the  gases  in  an  80  foot  coke  furnace 
and  a  37  foot  charcoal  furnace  shows  the  difference  very  clearly. 


226  Blast  Furnace. 

Coke  furnace.  Charcoal  furnace. 

CO.  COo  CO.  CO2 

Escaping  gases 29. r>  11.0  17.18  15.42 

Wl/2  feet  from  top 34.1  2.2  

18  feet  from  top ...  1925  14. 7G 

39  feet  from  top 35.0  1.1  

25%  feet  from  top ...  18.44  14.70 

65  feet  from  top 35.9  0.5  

32  feet  from  top ...  20.92  13.20 

70%  feet  from  top 36.6  0.0  

341/3  feot  from  top ...  26.33  3.20 


The  small  percentage  of  CO2  at  depths  below  16  feet  in  the 
coke  furnace  shows  that  little  reduction  takes  place  in  those  levels, 
The  percentage  of  CO2  in  the  gases  of  the  charcoal  furnace  shows 
clearly  that  reduction  is  not  very  active  until  a  depth  of  32  feet 
is  reached.  Between  that  level  and  the  hearth,  the  reduction  is 
very  active  and  is  necessarily  very  sudden,  as  over  80  per  cent, 
takes  place  in  the  last  five  feet  of  the  journey.  In  some  instances 
it  has  been  observed  that  reduction  in  the  charcoal  furnace  had 
not  even  begun  at  a  depth  of  30  feet.  Not  only  is  the  action 
postponed,  but  its  actual  occurrence  is  different.  We  have  seen 
that  the  action  of  CO  in  the  coke  furnace  produces  metallic  sponge 
direct.  In  the  charcoal  furnace,  metallic  iron  does  not  appear 
until  the  reduction  has  proceeded  for  some  time  and  the  lower 
oxides  of  iron  form  intermediate  steps  in  the  operation  as  shown 
by  expei  nnents  by  Ebelmen,  who  lowered  ores  into  the  furnace 
in  a  closed  box  which  was  withdrawn  for  examination. 

Time,  Depth,                                           f — First  experiment. — ^  ^-Second  experiment.-^ 

hours,  feet.           Temperature.            Fe^O3.      FeO.          Fe.  Fe2O3.       FeO.         Fe. 

2            8          Black    ..63.4            3.2            0.0  37.0           Tr.            0.0 

4V£      14%      Dull   red 33.0          32.5            0.0  27.8          12.7           0.0 

5Va      16%      Cherry   red 26.0         41.8            Tr.  24.1          17.5          0.0 

6V2      18%      W.  I.  softens 0.0         35.0         26.7  0.0         30.2        10.0 

Fuel  Consumption — The  fuel  consumption  in  a  charcoal 
furnace  is  usually  less  than  that  in  a  coke  furnace,  even  when- 
cold  blast  is  used.  This  is  largely  due  to  the  fact  that  since  the 

ratio  of  is  usually  very  low,  the  fuel  is  better  utilized.     Such 

CO2 

a  low  ratio  is  made  possible  by  the  fact  that  the  ore  does  not 


Action   Within  the  Furnace.  227 

depend  entirely  upon  CO  for  its  reduction.  It  is  to  be  noticed 
that  reduction  takes  place  at  temperatures  where  solid  carbon  can 
take  up  oxygen  from  the  ore.  Morover,  the  quantity  of  CO2  in 
the  top  of  the  furnace  is  sufficient  to  retard  reduction  greatly, 
while  it  is  usually  too  small  to  be  formed  by  the  action  of  CO  alone 
on  the  ore.  These  facts  point  to  the  probability  that  there  is 
a  considerable  amount  of  reduction  of  ore  by  solid  carbon  in  the 
lower  furnace  and  that  the  resulting  CO  performs  additional  re- 
duction in  the  cooler  parts  of  the  furnace,  thereby  doing  double 
duty.  An  additional  cause  for  the  low  fuel  consumption  rests  in 
the  fact  that  the  lessened  volume  of  blast  needed,  owing  to  the 
reaction  between  the  solid  carbon  and  fixed  oxygen,  permits 
slower  travel  through  the  cold  stock  and  hence  more  thoroughly 
cooled  gases.  Owing  to  the  lack  of  reduction  in  the  top  of  the 
furnace  there  is  no  evolution  of  heat  there.  The  temperature  of 
gases  escaping  from  a  charcoal  furnace  has  been  recorded  as  low 
as  117  degrees  F.  for  a  week  at  a  time.  Finally,  the  rapid  driving 
of  charcoal  furnaces  permits  the  passage  of  stock  through  the 
furnace  at  such  a  rate  that  loss  by  radiation  per  ton  of  product  is 
materially  lessened. 

SOURCES    OF   ECONOMY. 

The  function  of  the  blast  furnace  is  the  recovery  of  the  iron 
in  the  charge  with  as  little  expenditure  as  possible.  The  smelting 
charges  are  made  up  of  the  cost  of  the  materials,  and  the  cost 
of  handling  them  and  the  products.  The  cost  of  materials  and 
labor  are  fixed  by  the  natural  conditions  and  do  not  allow  much 
latitude  to  the  furnacemen.  The  quantity  of  materials  used, 
except,  perhaps,  in  the  case  of  fuel,  bears  a  constant  ratio  to  the 
output.  There  is,  therefore,  not  much  opportunity  for  saving, 
except  in  the  consumption  of  fuel. 

The  quantity  of  fuel  used  in  smelting  iron  always  depends 
upon  several  factors.  It  is  influenced,  primarily,  by  the  degree  of 
oxidation  to  which  its  carbon  is  burned.  The  smaller  the  ratio 

CO 

,  the  greater  the  quantity  of  carbon  that  is  burned  to  CCX, 

by  which  the  maximum  quantity  of  heat  is  developed.     In  the 
second  place,  the  more  effectively  the  products  of  combustion  are 


228  Blast  Furnace. 

cooled,  the  more  of  the  heat  developed  will  serve  a  useful  purpose. 
Well-cooled  gases  can  be  attained  only  by  having  a  long  pathway 
of  cold  materials  through  which  they  move  slowly.  Thirdly, 
since  the  losses  of  heat  by  radiation  and  conduction  are  functions 
of  time  and  not  of  yield,  the  more  rapidly  the  materials  pass 
through  the  furnace,  the  less  will  be  the  loss  of  heat  per  ton. 
This  condition  can  be  best  attained  by  rapid  driving.  Finally,  the 
more  heat  that  can  be  introduced  into  the  furnace,  without  the 
aid  of  fuel,  the  less  fuel  will  be  needed.  Hence,  a  well  heated 
blast  is  conducive  to  fuel  economy. 

The  effect  of  a  change  in  any  one  of  these  factors  is  cumula- 
tive. It  disturbs  the  equilibrium  that  exists  between  them  and 
compels  readjustment.  Any  cause  that  leads  to  a  decrease  in  fuel 
used,  necessarily  lessens  the  quantity  of  blast  needed,  and  hence, 
also,  the  quantity  of  escaping  gases.  In  consequence,  the  gases 
move  more  slowly,  give  up  more  heat  to  incoming  materials,  and 
pass  off  at  a  lower  temperature.  Since  there  is  less  carbon  in  the 
gases,  there  will  be  less  escaping  CO.  As  the  quantity  of  CO2  per 

ton  is  fairly  constant,  less  CO  means  a  lower  ratio,  -„-- .   The  less 

the  quantity  of  blast,  the  more  thoroughly  it  will  be  heated  by  the 
heating  arrangements,  which  brings  a  further  reduction  in  fuel. 
The  less  blast  needed  per  ton  of  pig,  the  more  tons  can  be  made  by 
a  given  capacity  of  equipment  in  a  given  time  and  the  less  will  be 
the  radiation  and  conduction  losses.  For  these  reasons,  a  seem- 
ingly slight  change  of  conditions  frequently  brings  a  surprisingly 
large  difference  in  results. 

Effect  of  Furnace  Height — Other  things  being  equal,  the 
height  of  a  furnace  has  a  profound  effect  upon  its  economical 
operation.  The  first  result  of  an  increase  of  height  of  a  small 
furnace  is  a  more  thorough  cooling  of  the  escaping  gases.  This 
will  permit  a  lessened  quantity  of  fuel  and  flux,  hence,  less  slag 
to  be  melted,  and  more  thorough  combustion  of  the  carbon.  The 
increase  of  blast  temperature  gives  identical  results.  The  effects 
of  increased  height  of  furnace  and  increased  blast  temperature 
are  shown  by  the  following  comparative  table : 


Action   }}7it1iiu  the  Furnace. 


229 


(2) 

48  feet. 
6,000 
905°  F. 
806  °F. 
28.50  cwt. 
16.00  cwt. 
48.00  cwt. 
31.00  cwt. 
120.0.")  cwt. 
168.37  cwt. 
1.336 
-220  tons. 
104,336  cal 

(3) 
80  feet. 
15,000 
905°  F. 
590°  F. 
22.50  cwt. 
11.  00  cwt. 
48.00  cwt. 
28.00  cwt. 
100.41  cwt. 
335.20  cwt. 
1.346 
350  tons. 
.    91,194  cal 

(4) 
80  feet. 
15,000 
1,300°  F. 
482°  F. 
19.99  cwt. 
11.  00  cwt. 
48.00  cwt. 
28.00  cwt. 
87.15  cwt 
119.47  cwt. 
1.371 
350  tons. 
.  88,577  cal. 

(5) 
90  feet. 
33,500 
1,310°  F. 
432°  F. 
19.69  cw.t. 
10.50  cwt. 
48.00  cwt. 
28.00  cwt. 
84.01  cwt. 
115.89  cwt. 
1.37S 
700  tons. 
85,912  cal. 

(1) 

Height    of   furnace....    48  feet. 
Cubic  feet  capacity.  .  .  .     6,000 
Temperature    of    blast.  .770°  F. 
Temperature  of  gases.. 844°  F. 
Wt.  coke  per  ton  pig.  .    40.76  cwt. 
Wt.  ston.'>  per  ton  pig.  18.25  cwt. 
Wt.  ore  per  ten  pig.  .  .    46.20  cwt. 
Wt.  slag  per  ton  pig.  .    34.15  cwt. 
Wt.  blast  per  ton  pig.  180.46  cwt. 
Wt.  gases  per  ton  pig.233.92  cwt. 
Ratio  gases  to  blast..      3.296 

Output 90  tons. 

Heat   requirement. . .  .111,180  cal. 

By  comparing  (i)  with  (2),  and  (3)  with  (4),  it  may  be 
observed  that  increased  blast  temperature  in  otherwise  similar 
furnaces  resulted  in  decreased  fuel  consumption  and  consequently 
a  decrease  in  blast,  flux,  waste  gases,  and  slag.  By  comparing 
(2)  with  (3)  and  (4)  with  (5)  it  may  be  seen  that  increase  in 
height  of  furnaces  results  in  increased  output,  cooler  gases  and 
lessened  fuel,  flux,  blast  and  waste  gases.  Of  course,  added  height 
will  be  of  no  avail  unless  the  furnace  be  kept  full.  Allowing  the 
stock  to  settle  will  result  in  increased  fuel  consumption. 

Limits  of  Size. — It  would  seem,  therefore,  as  if  a  continual 
increase  of  height,  ad  infinitum,  would  result  in  a  continued  fuel 
economy.  Such  might  be  the  case  if  it  were  not  for  the  fact  that 
the  complete  cooling  of  the  gases  is  rendered  impossible  because 
the  reduction  of  the  ore  is  exothermic  in  nature.  It  is  con- 
sequently useless  to  attempt  to  cool  the  gases  below  the  tem- 
perature that  will  be  attained  by  the  process-of  reduction.  It  is 
evident,  therefore,  that  the  maximum  saving  of  waste  heat  will 
be  reached  when  the  column  of  intercepting  materials  between  the 
hearth  and  the  point  where  reduction  by  CO  ceases,  is  long 
enough  to  cool  the  gases  to  the  temperature  of  the  reaction ;  in 
other  words,  when  the  zone  of  interception  is  sufficiently  long1 
to  remove  the  zone  of  reduction  beyond  the  influence  of  the  hearth 
temperature.  From  the  above  comparisons,  Bell  concluded  that 
there  was  no  advantage  to  be  gained  by  increasing  the  height  of 
furnaces  beyond  80  or  90  feet,  and  recent  experience  with  fur- 
naces 100  feet  in  height  has  amply  confirmed  his  conclusions. 

It  is  only  logical  to  assume  that  the  size  of  a  furnace  should 
bear  a  definite  relation  to  the  hearth  area,  or  at  any  rate  to  the 


230  Blast  Furnace. 

amount  of  work  done  per  square  foot  of  hearth  area.  The 
of  size  in  a  furnace  is  to  enable  a  large  quantity  of  stock  to  be 
presented  to  the  hot  gases  in  order  that  as  much  of  their  heat  as 
possible  may  be  extracted.  It  is  evident,  then,  that  height  alone, 
or  breadth  alone,  does  not  determine  the  proper  relationship,  since 
it  is  manifestly  a  question  of  volume.  A  moment's  consideration, 
moreover,  will  reveal  the  fact  that  of  all  the  heat  used  in  the  fur- 
nace, that  portion  only  which  is  absorbed  by  the  charge  can  apply 
toward  the  melting  of  the  iron  and  slag.  Hence,  if  we  can  cause 
the  charge  to  intercept  enough  heat  during  its  passage  through 
the  furnace  to  fuse  the  products,  that  is  all  we  can  hope  to  ac- 
complish. The  proper  furnace  volume  per  square  foot  of  hearth 
area  will  evidently  vary  with  the  quantity  of  heat  developed,  but 
for  a  given  degree  of  activity  the  volume  may  be  determined  ap- 
proximately by  this  formula:  The  number  cubic  feet  of  stock 
needed  per  square  foot  of  hearth  area  = 

Heat  capy.  of  products  per  sq.  ft.  of  hearth  area  in  24  h. 
Heat  capy.  of  the  charge  per  cu.  ft. 

Let  us  assume,  for  example,  that  a  furnace  burns  6000  pounds 
of  coke  per  square  foot  of  hearth  in  24  hours,  thereby  pVoducing 
6000  pounds  of  pig  and  55  per  cent,  as  much  slag;  then  the 
amount  of  heat  which  can  reside  in  the  molten  products  of  one 
square  foot  of  hearth  area  in  24  hours  will  be : 

B.  T.  u. 

6,000  X   0.22   X  2,700  —    3,564,000 

3,300  X  0.30  X  3,000  = 2,970,000 


Total 0.534.000 

which  is  the  total  heat  capacity  of  the  molten  product  of  one 
square  foot  of  hearth  area  per  24  hours,  and^is  the  numerator  of 
the  fraction. 

The  heat  capacity  of  the  charge  per  cubic  foot  is  evidently 
the  heat  capacity  per  pound  multiplied  by  the  weight  per  cubic 
foot.  The  weight  of  the  charge  per  cubic  foot  may  be  found  as 
follows : 

100  pounds  coke  occupies 3.57  cu.  ft.  space. 

170  pounds   ore  occupies 1.13  cu.  ft.  space. 

50  pounds  stone  occupies 0.50  cu.  ft.  space. 

320  pounds  charge   occupies 5.20  cu.  ft.  space. 


Action  Within  the  Furnace.  231 

Each  cubic  foot  weighs—^—  —or  61.5  pounds  when  it  enters 

the  furnace.  In  the  early  part  of  the  descent,  however,  the  ore 
loses  its  water  and  much  of  its  oxygen ;  the  coke  loses  some  car- 
bon through  solution  by  CO2 ;  the  stone  loses  some  CO2  through 
decomposition.  During  the  greater  part  of  the  descent,  therefore, 
the  weights  of  the  members  of  the  charge  will  be  modified  as 
follows : 

Pounds. 

100  pounds  coke,  less  5.7  per  cent,  carbon  stolen,  equals 94.3 

170  pounds  ore,  less  30  per  cent.  O2  and  IJL.O,  equals 119.0 

f>0  pounds  stone,  less  42  per  cent.  CO2  evolved,  equals 29.0 

320  pounds  charge  is  modified  until  it  equals 242.3 

61.5    X  —  — -  —  46.6,  which  would  be  the  weight  per  cubic 

foot  of  the  descending  materials   if  they  occupied  the  original 

space.      As    they   compact    somewhat    upon   changing   form   the 

final  weight  per  cubic  foot  is  probably  not  far  from  50  pounds. 

The  heat  capacity  of  the  charge  per  pound  is  as  follows: 

Pounds.  B.  T.  II. 

Iron 1.00  X  0.2   X  2,700  = 540.0 

Gangue  0.55  X  0.3   X  3.000  — 495.0 

Coke  0.943  X  0.428  X  3,000  = 1,211.7 


2.493  2,246.7 

Whence—         ^  —  900  B.  T.  U.  absorbed  per  pound  of  charge. 
900  X  50  =  45,000  B.  T.  U.  absorbed  per  cubic  foot,  which 

is  the   denominator  of  the   fraction.     Whereupon  -  —  = 

45,000 

145,  which  is  the  number  of  cubic  feet  of  charge  needed  to  absorb 
the  quantity  of  heat  that  will  suffice  to  fuse  the  products  of  24 
hours  from  one  square  foot  of  hearth  area.  If  the  furnace  has 
a  bosh  area  two  and  one-half  times  that  of  the  hearth,  the  height 
of  the  column  of  stock  which  contains  145  cubic  feet  will  be 

^  •-:  83  feet. 
175 

For  a  furnace  which  passes  its  own  volume  of  material  every 
15   hours,  this   would   require  a  working  column   from  melting 

zone  to  reducing  zone  of  —    X  83  =  $2  feet.   Assuming  that  the 


232  Blast  Funua\ 

zone  of  fusion  is  15  feet  above  the  hearth  level  and  that  the  re- 
ducing zone  is  8  feet  deep,  and  the  bell  clearance  10  feet  more, 
the  total  height  of  the  furnace  should  be  15  +  52  +  8  +  10  = 
85  feet,  which  is  found  ample  in  practice.  The  volume  of  stock 
which  should  pass  the  hearth  in  24  hours  is  greatly  affected  by 
the  rate  of  combustion  and  the  rapidity  of  movement  of  the  stock. 
With  the  very  low  rate  of  combustion  of  3000  pounds  per  square 
foot,  as  in  the  case  of  anthracite,  the  heat  intercepting  zone  need 
not  be  over  20  feet  high,  and  the  furnace  is  therefore  required 
to  be  only  50  to  55  feet  in  height.  In  the  case  of  charcoal,  where 
the  furnace  may  empty  itself  several  times  in  24  hours,  a  lesser 
height  is  necessary  than  in  a  coke  furnace  to  present  the  requisite 
quantity  of  stock  to  cool  the  gases  satisfactorily. 

Rapid  Driving — Other  things  being  equal,  the  rapidity  with 
which  materials  pass  through  the  furnace  is  in  proportion  to  the 
quantity  of  blast  which  enters  the  furnace.  The  prime  requisite 
for  rapid  driving  is  that  the  fuel  should  be  porous,  so  that  it  may 
unite  readily  with  the  blast  and  develop  rapidly  the  heat  for  melt- 
ing. In  the  second  place,  it  is  necessary  that  the  charge  should 
be  permeable  to  gases,  and  the  ores  readily  reducible,  in  order 
that  they  may  come  down  to  the  hearth  in  the  proper  condition 
for  melting.  The  furnace  hearth  should  be  large,  so  that  the 
materials  may  readily  present  themselves  for  fusion,  and  the  bosh 
should  be  steep  to  prevent  any  sticking  or  hesitancy  in  the  de- 
scent of  materials  in  the  zone  of  fusion.  Finally  the  ores  should 
be  rich  in  iron,  in  order  that  too  much  space  may  not  be  occu- 
pied by  unproductive  substances. 

Regularity — The  state  of  affairs  that  probably  conduces 
most  to  fuel  waste  is  irregular  working.  It  may  be  conveniently 
considered  as  synonymous  with  uneven  distribution  of  heat  from 
point  of  either  time  or  place.  If  the  proper  quantity  of  fuel  is 
charged  in  a  furnace,  and,  for  any  cause,  an  undue  proportion 
of  it  arrives  in  the  zone  of  combustion  at  one  time,  there  will  evi- 
dently be  at  some  subsequent  time  a  deficit  which  must  be  cor- 
rected by  extra  additions.  Or,  if  through  a  difference  of  per- 
meability, the  gaseous  current  is  directed  to  one  part  of  the 
charge  to  the  exclusion  of  the  others,  or  if,  through  the  break- 
ing of  water  connections  or  other  causes,  local  cooling  is  set  up, 


Action   Within  the  Furnace.  233 

the  ultimate  corrective  must  be  the  supplying'  of  the  deficit  by 
additional  fuel.  For  these  reasons,  the  materials  which  compose 
the  charge  should  be  introduced  with  due  regard  to  uniformity 
of  composition  and  regularity  of  descent. 

Stock  Distribution. — One  of  the  chief  causes  of  difficulty 
in  maintaining  uniformity  of  distribution  and  descent  of  stock  is 
the  mixing  of  coarse  and  fine  materials.  When  a  mixture  of  ma- 
terials of  differing  sizes  is  poured  in  a  heap,  it  usually  happens 
that  the  finer  portion  forms  a  cone,  whose  slopes  make  an  angle 
of  about  40  degrees  with  the  horizontal,  while  the  lumps  roll 
down  and  form  a  ring  at  the  base.  Applying  this  principle  to 
the  filling  of  a  blast  furnace,  we  see  at  once  that  if  the  distrib- 
uting bell  is  too  large,  or  if  the  stock  gets  low  in  the  furnace, 
the  charge  will  be  deposited  against  the  walls  and  the  lumps  will 
collect  in  the  hollow  at  the  center  and  form  a  central  column  of 
undue  permeability.  On  the  other  hand,  a  bell  that  is  too  small 
will  deposit  the  material  in  a  ring,  and  the  lumps  will  roll  to  the 
walls  as  well  as  toward  the  center,  leaving  an  annular  column 
which  will  be  relatively  impervious  to  the  gases.  The  ideal  con-% 
dition  would  be  to  distribute  the  materials  so  that  they  would  be 
uniformly  mixed.  The  best  effects  are  obtained  when  the  dis- 
tributing bell  has  a  diameter  4  or  5  feet  less  than  the  stockline, 
thereby  leaving  2  to  2.^/2  feet  clearance  on  all  sides  of  the  bell. 


CHAPTER  VI. 
FURNACE  IRREGULARITIES. 

A  blast  furnace  in  operation  is  subject  to  many  forms  of  ir- 
regularities, which  are  due  to  a  variety  of  causes.  As  a  rule, 
such  irregularities  need  to  be  detected  promptly,  diagnosed  accu- 
rately and  acted  upon  immediately,  in  order  that  the  furnace  out- 
put may  not  suffer,  or,  indeed,  the  safety  of  the  furnace  may  not 
be  endangered.  The  ability  to  recognize  the  first  symptoms  of  dis- 
order and  thereby  to  counteract  or  prevent  the  train  of  evils  that 
usually  follows,  is  an  invaluable  asset  to  the  successful  furnace 
manager.  This  ability  is  acquired  only  by  long  experience  and 
close  attention,  supplemented  by  a  natural  aptitude  for  discern- 
ing that  which  is  not  always  distinctly  indicated. 

LEAKY   TUYERES. 

The  most  common  trouble  to  which  a  furnace  is  subject  is 
probably  leaky  tuyeres.  A  leaky  tuyere  results  usually  from 
wear  or  from  local  superheating  or  "  burning  "  of  the  metal, 
whereby  the  cooling  water  is  allowed  to  leak  into  the  furnace 
hearth.  If  the  leak  is  not  promptly  discovered  and  stopped,  it 
may  result  in  serious  cooling  of  the  hearth.  The  leak  may  occur 
in  any  part  of  the  tuyere,  but  the  most  vulnerable  point  is  the 
tip  of  the  nose,  and  especially  the  upper  surfaces.  It  may  be  due 
to  abrasion  of  the  constantly  descending  stock  during  a  long 
period  of  service,  which  wears  the  metal  so  thin  that  it  cracks 
under  the  strain.  More  frequently,  probably,  the  damage  is 
caused  by  a  stoppage  of  the  flow  of  cooling  water,  whereby  the 
enclosed  water  is  converted  into  steam  at  the  hottest  point,  and 
the  integrity  of  the  metal  destroyed  through  superheating.  An- 
other cause  of  burning  is  the  alloying  of  molten  iron  which  drops 
on  the  tuyeres  in  its  passage  toward  the  hearth,  or  is  directed 
toward  them  too  constantly  by  some  obstruction.  The  burned 
tuyeres  that  so  frequently  follow  the  dislodgment  of  scaffolds 
probably  result  from  the  splashing  against  them  of  molten  iron. 


furnace  Irregularities.  235 

Detection  of  Leaks — There  are  several  ways  in  which  a 
leaky  tuyere  becomes  manifest.  Occasionally  it  is  announced  by 
a  loud  report  like  an  explosion,  or  by  the  increased  volume  and 
inflammability  or  "  wildness  "  of  the  escaping  gases.  More  often, 
however,  it  is  suspected  from  its  effect  upon  the  escaping  prod- 
ucts of  fusion.  The  cinder  becomes  dark,  shows  a  black  crust 
or  appears  foamy  or  glassy.  At  the  same  time  the  sulphur  in 
the  iron  runs  up,  showing  that  the  hearth  is  abnormally  cool. 
When  a  leak  is  suspected,  its  existence  may  be  verified  by  inves- 
tigation. Sometimes  dampness  can  be  seen  about  the  base  of 
the  tuyere  or  cooler.  A  cold  bar  thrust  in  at  the  peep  hole  will 
generally  show  dampness  when  withdrawn  if  there  is  a  leak. 
Tongues  of  blue  flame  may  break  through  the  walls  about  the 
tuyere.  Sometimes,  water  can  be  seen  by  looking  into  the  tuyere, 
particularly  if  the  blast  be  thrown  off.  If  the  water  inlet  of  the 
tuyere  be  shut  off,  the  gases  from  the  hearth  will  work  into  the 
leak  and  can  be  ignited  by  a  torch  at  the  discharge  pipe. 

Changing  Tuyeres — When  the  presence  of  a  leaky  tuyere 
has  been  established,  no  time  should  be  lost  in  replacing  it.  The 
usual  method  of  extracting  a  tuyere  is  to  stop  the  blast,  remove 
the  blowpipe,  insert  a  tuyere  hook,  and  by  means  of  a  claw  in 
the  hands  of  several  lusty  helpers,  to  jar  the  tuyere  loose.  Occa- 
sionally it  becomes  so  expanded  by  heat  while  leaking  that  it 
binds  in  the  cooler  and  vigorously  resists  extraction.  Sometimes 
this  condition  may  be  overcome  by  slacking  the  water  in  the 
cooler  and  allowing  it  in  turn  to  expand  enough  through  heating 
to  release  the  tuyere.  As  a  last  resort  it  may  be  necessary  to  melt 
the  tuyere  completely  out  by  means  of  an  oil  blowpipe.  As  soon 
as  it  is  removed,  a  new  one  which  has  previously  been  filled  care- 
fully with  water  and  all  air  removed,  is  thrust  into  place,  wedged 
tightly  by  blows  from  a  dolly  and  the  water  connections 
promptly  made.  The  blowpipe  is  then  replaced  and  the  blast 
turned  on.  Every  minute  spent  in  replacing  a  tuyere  is  dead  loss 
to  the  furnace,  since  the  blast  must  be  stopped  entirely  during 
the  change.  The  time  of  changing  should  not  be  over  6  minutes, 
but  frequently  takes  10  to  20. 

Causes  of  Burning.— Ordinarily  a  well  cooled  tuyere  with 
a  positive  water  circulation  will  resist  the  heating  effect  of  small 


236  Blast  Furnace. 

quantities  of  molten   iron.     Molten  slag  will   not  affect  bronze 
unless  it  carries  shots  of  iron.     There  are  several  ways  in  which 

jftJavJjSl  the  dripping  iron  may  burn  the  tuyeres.  Sometimes  the  molten 
material  cuts  grooves  above  them,  or  is  deflected  by  some  ob- 
struction, so  that  a  small  stream  of  iron  impinges  constantly  on 
the  same  spot  in  the  tuyere,  thereby  weakening  it  and  heating 
it  to  the  steaming  point.  L,umps  of  fuel  or  chilled  cinder  lying 
before  the  tuyeres  may  deflect  the  iron  against  them  and  cause 
damage.  A  persistent  obstruction  should  be  removed  by  a 
pricker.  Ores  containing  lead  or  zinc  may  cause  trouble  because 
of  the  readiness  with  which  those  metals  alloy  with  bronze. 

If  the  blast  enters  through  the  tuyere  under  good  pressure 

and  penetrates  directly  to  the  hearth  center,  there  is  little  action 

immediately  above  the  tuyeres  and  an  accumulation  of  material 

frequently  forms  on  the  nose  of  each  tuyere  and  protects  it  from 

iron  Age    tne  dripping  iron.     If  the  water  supply  is  suitable,  the  repeated 

Feb.  21,1901.    JQSS  Q£  a  tllyere  indicates  irregular  working. 

The  sudden  stoppage  of  the  blast  when  the  hearth  is  full  is 
always  a  source  of  danger  to  tuyeres,  since  it  allows  slag  and 
metal  to  flow  into  them  when  the  pressure  is  removed.  Before 
throwing  off  the  blast,  the  cinder  should  always  be  flushed  if 
possible.  If  it  is  near  casting  time,  it  may  be  advisable  to  open 
the  tapping  hole  also. 

Prevention  of  Burning — There  appears  to  be  no  regular 
means  of  preventing  burned  tuyeres,  except  when  they  are  caused 
by  water  stoppage.  Water  stoppage  is  due  to  obstructing  par- 
ticles carried  in  the  water  supply.  A  tolerably  pure  water  should 
be  used,  and  passed  through  a  screen  to  remove  sticks,  leaves, 
fishes,  etc.,  before  it  enters  the  tuyeres.  A  pressure  of  25  pounds 
per  square  inch  will  generally  suffice  to  keep  fine  sediment  in 
motion.  A  higher  pressure  of  water  or  steam  should  be  used 
periodically  to  wash  out  any  accumulations  that  may  have 
formed.  This  should  be  done  regularly  every  day  or  week  ac- 
cording to  the  quality  of  water  used.  Higher  pressures  should 
not  be  used  regularly,  as  experience  shows  that  tuyeres  that  are 
successfully  protected  by  a  pressure  of  25  pounds  will  burn  fre- 
quently with  40  pounds.  It. is  suggested  that  water  at  such  high 


Furnace  Irregularities.  237 

pressure  striking  against  the  nose  of  the  tuyere,  bounds  away 
without  allowing  sufficient  period  of  contact  to  cool  it  properly. 
Other  Coolers. — Bosh-plates  and  tuyere  coolers  are  sub- 
ject to  similar  vicissitudes,  but  their  destruction  is  far  less  fre- 
quent, as  they  are  less  exposed  to  attack  from  the  molten  iron. 
The  cinder-notch  cooler  and  intermediate  cooler  are  also  com- 
paratively safe  from  trouble.  The  monkey,  however,  is  occa- 
sionally attacked  by  a  molten  iron  which  may  present  itself  at 
that  level  with  a  viscous  cinder  or  when,  for  any  reason,  casting- 
has  been  delayed  too  long.  The  changing  of  the  monkey,  how- 
ever, is  a  comparatively  simple  operation,  and  is  subject  to  the 
same  principles  as  the  changing  of  the  tuyeres,  as  is  also  the 
changing  of  any  other  water-cooled  part  of  the  furnace. 

DESTRUCTION   OF   LINING. 

The  destruction  of  the  lining  at  any  point  in  the  furnace 
above  the  melting  zone  will  result  in  the  overheating  of  the  shell, 
and  the  formation  of  what  is  commonly  called  a  "  hot  spot."  If 
the  lining  is  destroyed  within  the  melting  zone,  the  molten  ma- 
terial may  eat  through  the  outer  shell  and  a  "  break-out  "  result. 

The  lining  of  a  blast  furnace  is  subject  to  a  great  variety  of 
conditions  throughout  its  course.  Its  temperature  ranges  from 
a  little  above  boiling  water  to  the  melting  point  of  platinum,  and 
its  surface  is  subjected  to  the  abrasion  of  the  countless  angles 
of  solid  stock  and  to  the  fluxing  and  disintegrating  action  of 
thousands  of  tons  of  molten  matter,  as  well  as  the  corrosive  ac- 
tion of  the  gases.  According  to  Liirmann,  there  are  four  distinct 
agencies  at  work  tending  to  destroy  the  furnace  lining. 

1 i )  The  abrasion  of  the  descending  solid   materials,   which 
affects  all  depths  above  the  zone  of  fusion. 

(2)  The  action  of  certain  constituents  of  the  gases,  notably 

CN  and  its  salts,  which  are  volatile  at  depths  below  20  feet.  }"$•  four< 

(3)  The  action  of  NaCl  from  the  coke  in  forming  silicates   p-3J>7-' 
which  are  fusible  at  moderate  temperatures.   . 

(4)  The  deposition   of  carbon   around   spots   of  iron   which 
occur  in  the  bricks,  and  which  cause  disintegration,  especially  in 
the  tipper  part  of  the  furnace. 


238  Blast  Furnace. 

The  first  two  causes  are  undoubtedly  extremely  active  in  their 
respective  zones,  but  the  last  two  can  safely  be  neglected  if  they 
exist  at  all. 

The  carbonization  of  the  bricks  below  the  fusion  zone  tends 
to  protect  them  by  offering  to  the  corrosive  effect  of  the  cinder 
a  substance  which  is  neutral  to  both  acids  and  bases.  It  is  prob- 
able that  no  bricks  could  long  withstand  the  furnace  conditions 
without  this  protection.  The  carbonization  of  the  lining  appears 
to  be  most  rapid  under  the  influence  of  a  hot,  limey  cinder,  which 
is  an  additional  reason  for  blowing  in  hot  and  limey,  so  that  the 
protecting  condition  may  be  produced  as  early  as  possible.  The 
carbonizing  of  the  lining  led  to  the  suggestion  of  using  carbon 

Tr.A.  I.  M.  E., 

XXL,  112.    bricks,  but  they  have  never  come  into  general  use. 

For  the  protection  of  the  bosh  walls,  which  is  the  most  vul- 
nerable part  of  the  furnace,  bosh-cooling  plates  are  in  almost  uni- 
versal use.  They  preserve  the  proper  shape  of  the  walls,  thereby 
prolonging  the  blast,  decreasing  the  fuel  consumption  and  in- 
creasing the  output. 

Hot  Spots. — With  the  introduction  of  automatic  charging, 
the  hot  spot  assumed  a  new  importance.  It  was  soon  found  that 
furnaces  charged  with  a  self-dumping  skip  usually  developed  a 
hot  spot  on  the  shell  about  20  feet  above  the  top  of  the  bosh  and 
usually  on  the  side  opposite  the  skipway,  within  a  few  weeks 
after  blowing  in.  It  is  generally  assumed  that  this  is  the-  effect 
of  the  channeling  of  the  gases  through  the  lumpy  portion  of  the 
materials  which  are  thrown  to  that  side.  A  similar  effect  will 

Tr.^i.M.^K,  result  from  an  improperly  proportioned  bell,  since  the  lumps  al- 
ways roll  to  the  lowest  level,  and  the  fines  remain  behind,  form- 
ing peaks  or  ridges  immediately  below  the  point  of  discharge. 
As  a  result,  automatic  chargers  have  been  pretty  uniformly  sup- 

xxxv1;  ^'224!  plemented  by  stock  distributors.  The  fact  that  they  have  gen- 
erally succeeded  in  mitigating  this  difficulty  shows  pretty  con- 
clusively that  it  is  due  to  the  irregular  distribution  of  the  furnace 
action.  Since  the  Ipcation  of  the  trouble  is  generally  far  above 
the  usual  zone  of  fusion,  it  is  evident  that  if  the  action  is  due  to 
fluxing  of  the  lining,  it  must  result  in  a  very  easily  fused  silicate, 
which  points  to  action  by  the  alkalis.  This  theory  is  supported 


Furnace  Irregularities.  239 

by  the  fact  that  the  level  corresponds  to  that  of  the  decomposi- 
tion of  the  cyanides  and  the  formation  of  alkaline  carbonates. 

Breakouts.  — A  breakout  resulting  from  destruction  of  the 
lining,  may  occur  at  any  point  below  the  limits  of  fusion,  but 
does  not  assume  a  very  serious  significance  unless  it  occurs  below 
the  surface  of  the  metal  lying  molten  in  the  hearth.  The 
emission  of  iron  or  cinder  around  the  coolers  is  not  fol- 
lowed by  any  considerable  body  of  matter,  and  may  be  read- 
ily checked  by  chilling  with  water  from  a  hose.  If  the  break- 
out occurs  at  the  tapping-hole,  the  iron  should  be  directed  into 
the  pig-beds,  or  other  suitable  depressions,  so  that  it  can  be  read- 
ily broken  and  handled.  Sometimes  breakouts  find  their  way 
through  the  foundations  to  some  distance  and  rise  through  the 
floor  around  the  furnace,  where  they  must  be  relieved  by 
promptly  tapping  the  furnace.  Breakouts  are  never  due  to  the 
erosion  of  the  hearth  lining,  because  iron  is  not  active  in  disin- 
tegrating brick.  They  can  occur  only  when  the  brickwork  be- 
comes disrupted  from  any  cause,  such  as  expansion,  thereby  leav- 
ing a  passage  to  the  unprotected  shell.  They  may  be  prevented 
by  properly  jacketing  and  binding  the  hearth  wall,  to  prevent 
movement.  Frequently  they  stop  themselves  by  chilling  in  the 
cracked  brickwork  before  they  reach  the  jacket.  Water-cooled 
jackets  or  heavy  uncooled  jackets  having  large  thermal  capacity 
will  chill  incipient  breakouts,  thereby  checking  them  before  they 
become  dangerous. 

OBSTRUCTIONS. 

Several  different  types  of  furnace  obstructions  may  be  dis- 
tinguished as  occurring  at  different  levels  of  the  furnace  and 
being  due  to  different  causes. 

Pillaring Pillaring  is  a  phenomenon  peculiar  to  the  hearth, 

and  is  the  result  of  faulty  blast  distribution.  If  the  penetration 
of  the  blast  is  insufficient,  there  is  liable  to  be  a  conical  pillar  of 
cold  stock  extending  up  through  the  middle  of  the  hearth  and 
surrounded  by  an  annular  column  of  activity.  The  presence  of 
the  pillar  has  been  proven  in  some  instances  by  thrusting  a  bar 
across  the  hearth  from  tuyere  to  tuyere.  The  obstruction  could 
be  felt,  and  the  bar,  when  withdrawn,  was  red  at  each  end  with 


240  Blast  Furnace. 

a  black  middle  section.  An  increased  blast  volume  or  a  decreased 
tuyere  area  would  give  better  blast  penetration  to  such  a  hearth. 
Pillars  of  dead  material  may  accumulate  around  the  hearth 
between  tuyeres,  especially  if  the  tuyeres  are  far  apart  and  the 
blast  enters  under  good  pressure.  Such  pillars  are  not  neces- 
sarily detrimental.  They  may  be  reduced  in  size  by  increasing 
the  number  of  tuyeres. 

Scaffolds.  — Obstructions  which  have  their  origin  above  the 
hearth  and  depend  more  or  less  upon  the  furnace  walls  for  sup- 
port are  known  under  the  somewhat  general  term  of  "  scaffold." 
A  scaffolded  furnace  is  sometimes  said  to  be  "  hanging/'  an  ex- 
pression which  is  derived  from  the  fact  that  charges  refuse  to 
descend  regularly  and  properly.  Scaffolds  are  very  prone  to 
occur  on  the  bosh  of  the  furnace,  where  they  have  their  origin  in 
incrustations  due  to  a  contraction  of  the  zone  of  fusion.  They 
occur  also  in  the  zone  of  reduction,  where  they  appear  to  be  due 
to  the  wedging  resulting  from  excessive  carbon  deposition.  Such 
conditions  result  in  frequent  slipping  of  the  stock,  causing  ir- 
regular quality  of  iron,  due  probably  to  the  accession  of  oxygen 
brought  in  by  the  sudden  precipitation  to  the  hearth  of  incom- 
pletely prepared  materials.  This  irregularity  is  far  reaching  in 
its  effects,  and  is  frequently  the  cause  of  much  of  the  "  seconds  " 
in  the  rail  mill. 

Incrustations  occur  at  the  top  of  the  fusion  zone.  If  for  any 
cause  the  zone  of  fusion  undergoes  contraction,  the  pasty,  par- 
tially melted  material  becomes  incrusted  and  adheres  together 
and  to  the  walls,  thereby  impeding,  and  sometimes  preventing 
descent.  The  partially  fused  condition  of  the  incrustation  may 
offer  very  great  resistance  also  to  the  passage  of  the  gases.  The 
contraction  of  the  zone  of  fusion  may  be  brought  about  by  sev- 
eral causes,  such  as  decrease  of  fuel  in  the  charge,  increase  of 
refractoriness  of  the  slag,  or  increase  of  moisture  in  the  blast,  on 
account  of  which  the  quantity  of  heat  developed  may  be  less  than 
the  requirements.  It  is  sometimes  caused,  also,  by  too  high  blast 
temperature.  This  naturally  brings  more  heat  into  the  hearth, 
but  may  also  cause  a  contraction  of  the  zone  of  fusion.  This  par- 
adox is  best  accounted  for  by  the  fact  that  the  activity  of  oxygen 
toward  carbon  increases  as  the  temperature  rises.  The  combus- 


Furnace  Irregularities.  241 

tiou   takes   place   sooner,   in   consequence,   and   is   proportionally 
more  intense  and  less  extended  in  area. 

The  best  indication  that  a  furnace  is  scaffolded  is  its  refusal 
to  take  charges  or  the  indication  of  the  gauges  that  the  stock 
does  not  sink,  or  else  sinks  more  rapidly  on  one  side.  The  blast 
pressure  usually  goes  up,  and  the  gas  becomes  thin,  hot  and 
scanty.  The  gas  flames  and  the  fumes  become  less  dense.  If  the 
obstruction  is  due  to  incrustation,  a  portion  of  cold  blast  will 
drive  the  zone  of  fusion  higher  and  will  tend  to  soften  the  ob- 
struction. Then  slacking  the  engines  and  opening  the  relief  valve 
will  frequently  let  the  obstruction  descend.  It  is  advisable  to 
give  the  furnace  blast  again  as  soon  as  the  obstruction  is  loosened, 
so  that  the  upward  pressure  may  form  a  cushion  to  prevent 
splashing  the  tuyeres  with  cinder  and  iron.  It  is  best  also  to 
open  the  bell  to  relieve  the  sudden  rush  of  gas  displaced  by  the 
falling  mass.  This  method  is  not  always  successful  at  first,  but 
a  second  or  third  trial  may  bring  results. 

Repeated  hangs  may  be  caused  by  too  much  limestone,  in  which 
case  they  may  be  relieved  by  reducing  the  quantity  of  stone  or  by 
charging  sand  or  sandy  scrap  over  the  scaffold.  Scrap  and  coke 
may  be  charged  on  an  obstruction,  but  stone  should  always  be 
avoided.  More  persistent  hangs  may  demand  more  strenuous  meas- 
ures. Various  methods  have  had  their  advocates.  A  method  consid- 
erably used  formerly  consisted  of  removing  the  cinder  notch  and 
cooler  and  by  means  of  a  full  blast,  blowing  out  through  the 
notch  all  of  the  stock  below  the  obstruction, "Thus  leaving  it  un- 
supported till  it  falls  under  the  weight  of  the  superimposed  ma- 
terial. An  obstruction  which  adheres  pertinaciously  may  be  re- 
moved by  a  charge  of  dynamite  or  by  local  combustion.  A  hole  Tr-  Aj£  **•  J- 
may  be  drilled  through  the  furnace  wall  back  of  the  obstruction 
and  a  tuyere  temporarily  introduced.  If  the  charge  at  the  point 
contains  insufficient  fuel,  an  oil  blowpipe  may  be  substituted. 
An  obstruction  which  has  formed  an  arch  across  the  furnace  and 
has  interrupted  all  passage  of  gas  or  stock  may  be  broken  up 
by  exploding  dynamite  above  it.  TrxAj  p  67oE'' 

Repeated  obstructions  of  the  same  nature  show  faulty  man- 
agement and  may  be  due  to  too  heavy  burden  or  improper  flux- 
ing. Scaffolds  may  be  sometimes  traced  to  faulty  furnace  de- 


242  Blast  Furnace. 

sign,  such  as  improper  bosh  angle  or  improper  size  of  bell.  In 
case  of  faulty  design,  the  remedy  lies  only  in  remodeling  the 
furnace. 

The  form  of  obstruction,  due  to  wedging  of  the  stock,  fre- 
quently occurs  in  the  zone  of  carbon  deposition  in  the  top  of  the 
Txxvi.M'E''  furnace.  It  has  been  shown  by  Laudig  that  the  weight  of  car- 
bon deposited  on  some  ores  may  exceed  the  weight  of  oxygen 
extracted  by  almost  50  per  cent.,  and  even  exceed  the  whole  ore 
in  volume.  In  his  experiments,  the  average  of  33  ores  of  various 
types  and  localities  showed  that  the  usual  deposition  of  carbon 
amounted  to  about  60  per  cent,  of  the  oxygen  extracted.  On  the 
assumption  that  90  per  cent,  of  the  oxygen  of  the  ore  is  extracted, 
in  the  zone  of  carbon  deposition,  we  would  expect  an  average 
deposition  of  23  pounds  of  carbon  for  each  100  pounds  of  pig, 
or  about  170  pounds  of  ore.  As  the  specific  gravity  of  the  ore 
is  several  times  greater  than  that  of  the  deposited  carbon,  it  ap- 
pears that  such  a  deposit  of  carbon  would  nearly  double  the  vol- 
ume of  the  ore.  Such  a  large  increase  of  volume  is  out  of  pro- 
portion to  the  usual  batter  of  furnaces  at  that  depth,  and  the 
inevitable  result  is  wedging.  The  carbon  also  fills  the  interstices 
between  the  pieces  of  stock,  and  prevents  the  proper  flow  of  the 
gases. 

When  the  stock  becomes  wedged  so  tightly  that  it  can  no 
longer  descend,  the  furnace  is  said  to  "  hang."  The  unwedged 
stock  beneath  continues  to  settle  and  ultimately  the  unsupported 
bridge  falls.  This  is  known  as  a  "  slip  "  and  is  usually  accom- 
panied by  an  "  explosion  "  of  greater  or  less  violence,  which  fre- 
quently ejects  considerable  quantities  of  stock  from  the  furnace 
and  occasionally  displaces  the  bell  and  hopper.  These  so-called 
explosions  are  not  of  the  nature  of  the  usual  phenomena  called 
by  that  name,  but  are  generally  somewhat  prolonged  blows,  as  if 
they  represented  merely  relief  from  an  accumulation  of  tolerably 
moderate  pressure,  rather  than  an  explosion  proper.  A  genuine 
explosion  sometimes  occurs  in  the  top  of  the  furnace,  when,  for 
any  reason,  air  is  drawn  in  in  sufficient  quantity  to  make  an  ex- 
plosive mixture  with  the  furnace  gases.  Such  an  explosion 
would  naturally  occur  in  the  open  space  above  the  stock,  and 
while  likely  to  damage  the  furnace,  could  hardly  eject  stock 


Furnace  Irregularities.  243 

which  lies  below  it.  Yet  stock  is  generally  ejected.  Sometimes 
as  much  as  three  charges  have  been  thrown  out,  and  there  is 
a  case  on  record  where  a  charcoal  furnace  was  practically 
emptied  by  this  action.  It  has  been  suggested,  therefore,  that  the 
explosion  might  be  due  to  sudden  reduction  of  the  ore  by  finely 
divided  carbon,  which  thereby  generates  rapidly  a  large  volume  of 
gas.  It  is  probable,  however,  that  a  true  explosion  well  down  in 
the  furnace  would  burst  the  shell  before  it  could  eject  such  a 
heavy  mass  of  superincumbent  materials.  The  suggestion  that 
the  effect  is  due  to  the  sudden  displacement  of  the  gases  on 
account  of  the  falling  mass  is  open  to  the  objection  that  some 
of  the  smallest  slips  show  the  greatest  power.  Moreover,  simple 
movement  of  a  confined  gas  does  not  necessarily  develop  an  in- 
creased volume  or  pressure.  The  true  explanation  is  probably 
embodied  in  the  theory  that  the  gases  are  trapped  until  the  pres- 
ence of  the  blast  is  sufficient  to  force  a  passage  and  some  of  the 
stock  is  carried  out  by  the  momentum. 

It  can  easily  be  shown  that  three  charges  of  stock  will  weigh, 
when  charged,  approximately  100,000  pounds,  and  in  a  fur- 
r.oce  having  a  15  foot  stock  line,  will  occupy  a  depth  of  about  10 
feet.  Through  loss  of  C,  O2  and  CO2,  this  stock  may  not  weigh 
more  than  90,000  pounds.  The  upward  pressure  of  the  gases  at 
that  point  when  a  blast  pressure  of  15  pounds  is  consumed  in  driv- 
ing the  gases  through  75  feet  of  stock  will  evidently  be  approxi- 
mately 2  pounds  per  square  inch,  which  exerts  a  total  upward 
pressure  of  about  51,000  pounds.  It  is  evident,  therefore,  that 
even  under  normal  conditions,  the  lifting  force  of  the  gases  at  10 
feet  depth  is  equal  to  more  than  half  the  weight  of  the  superin- 
cumbent charges. 

If,  then,  the  stock  beneath  continues  to  settle  until  a  gap  of 
10  feet  exists,  there  will  be  a  column  of  materials  only  55  feet  high 
for  the  blast  to  traverse.  If  this  resistance  uses  up  n  pounds  of 
the  initial  pressure,  there  will  be  left  4  pounds  pressure  at  the 
depth  of  10  feet,  which  is  double  that  before,  and  more  than 
enough  to  lift  bodily  the  whole  quantity  of  stock  above  it.  Con- 
sequently, it  breaks  through  the  weakest  point  in  the  wedge,  and 
the  suddenly  released  pressure  carries  some  of  the  stock  with 
it  put  of  the  furnace  and  lets  the  rest  fall  within.  This  assumption 


244  Blast  Furnace. 

is  based  upon  continuance  of  normal  pressure  in  the  engine  room. 
If  the  engine  speed  has  remained  constant,  and  the  pressure  has 
risen  in  consequence,  the  moment  when  the  accumulated  pressure 
will  force  a  passage  will  arrive  much  sooner. 

The  frequency  of  these  so-called  top-explosions  was  greatly  in- 
creased by  the  use  of  high  percentages  of  Mesaba  ore.  The 
trouble  was  naturally  attributed  to  the  fine  state  of  division  of  the 
ore,  since  that  was  its  most  marked  peculiarity.  However,  it  is 
observed  that  finely  divided  magnetic  concentrates  do  not  cause 
slips  and  explosions  in  anything  like  the  way  that  Mesaba  ores 
do.  When  it  is  recalled  that  the  Mesaba  ores  deposit  by  far  the 
most  carbon  of  any  ores  known,  while  magnetites  deposit  little 
if  any,  this  fact  confirms  the  opinion  that  the  difficulty  is  due  not 
so  much  to  fineness,  per  se,  as  to  resistance  of  deposited  carbon. 
Prevention  of  Wedging — The  wedging  due  to  carbon  de- 
position can  be  prevented  by  avoiding  ores  that  are  active  in  sep- 
arating carbon.  If  such  ores  must  be  used,  means  for  prevention 
of  this  pernicious  activity  should  be  adopted.  It  has  been  observed 
^at  ^ie  use  °f  m&h  percentages  of  limestone  has  this  effect.  For 
p-6-  example,  a  furnace  which  gave  trouble  with  21  per  cent,  of  stone, 
ran  very  smoothly  on  27  per  cent.  The  most  obvious  explanation 
of  this  fact  is  that  the  solvent  power  of  the  additional  30  per  cent, 
of  CO2  which  was  evolved,  was  sufficient  to  dissolve  enough  de- 
posited carbon  to  enable  the  gases  to  keep  an  open  passageway, 
whereas  the  lesser  amount  could  not.  Again,  it  has  been  observed 
that  stone  crushed  to  small  sizes  is  not  as  efficient  in  this  respect 
as  large  stone.  A  furnace  which  ran  smoothly  on  30  per  cent, 
uncrushed  stone,  immediately  gave  trouble  when  the  stone  was 
crushed  to  pass  a  4  inch  ring.  It  is  not  improbable  that  the  COa 
was  evolved  from  the  smaller  pieces  too  high  in  the  furnace  to 
exert  its  full  solvent  power. 

CHILLED    HEARTH. 

A  chilled  hearth  is  probably  the  most  serious  disorder  that 
can  befall  a  furnace.  It  may  have  its  origin  in  any  cause  that 
does  not  leave  enough  heat  in  the  hearth  to  keep  its  contents  fluid. 
This  condition  may  result  from  an  insufficient  supply  of  fuel,  or 
from  a  suddenly  increased  demand  upon  the  regular  supply,  such 


Furnace  Irregularities.  245 

as  leaking  water  coolers  or  excessive  moisture  in  the  blast ;  or  it 
may  result  from  the  sudden  precipitation  into  the  hearth  of  a 
mass  of  material  from  a  colder  part  of  the  furnace.  When  the 
hearth  chills,  the  iron  and  cinder  become  solid  either  wholly  or  in 
part,  which  makes  tapping  in  the  usual  way  impossible.  The  only 
remedy  is  to  raise  the  temperature  of  the  hearth  to  the  melting 
point  as  soon  as  possible. 

Detection  of  Chill — When  chilling  is  due  to  a  too  heavy 
burden,  or  to  too  moist  blast,  the  effect  is  gradual  and  may  be 
foreseen.  The  signs  are  a  cold  cinder  and  cold  iron,  dark  tuyeres, 
chilled  cinder  notch  and  tuyeres.  By  promptly  charging  a  coke 
blank,  the  condition  may  be  corrected  before  very  serious  results 
occur. 

When  the  chilling  is  due  to  copious  water  leaking,  or  to  a 
slip,  the  effect  may  be  so  sudden  as  to  preclude  the  possibility  of 
prevention.  A  chill  caused  by  a  small  amount  of  water  leaking 
into  the  front  of  the  furnace  will  give  rise  to  a  hard  tapping  hole. 
If  the  leak  is  not  large,  the  hardness  may  be  evident  only  after 
the  blast  has  been  shut  off  for  a  while.  The  chilling  may  not  be 
serious,  simply  lengthening  the  time  necessary  to  open  the  tap- 
ping hole.  If  it  is  impossible  to  open  the  hole,  preparation  must 
be  made  to  tap  iron  through  the  cinder  notch.  The  system  of 
coolers  must  be  removed  and  a  temporary  runner  of  bricks  and 
clay  constructed. 

Remedy  for  Chill — After  a  temporary  system  of  casting 
through  the  cinder  notch  has  been  established,  the  tapping  hole 
may  be  opened  up  by  some  auxiliary  system  of  melting.  The  time- 
honored  method  is  by  means  of  the  oil  blow  pipe,  which  is  a  device 
for  spraying  inflammable  oil  by  means  of  an  air  blast.  A  3  inch 
pipe,  tapped  from  the  bustle  pipe  or  tuyere  stock  by  means  of  a 
flexible  connection,  conveys  the  air,  and  a  ^  inch  pipe  led  into  XV.,P.*«J! 
the  3  inch  pipe  through  a  reducing  flange,  is  connected  with  an 
elevated  supply  of  oil.  The  blast  breaks  up  the  drops  of  oil  into 
a  fine  spray,  which  burns  with  the  oxygen  of  the  blast,  producing 
a  very  high  temperature,  which  is  sufficient  to  melt  the  material  iwd, 
c'hilled  in  the  tapping  hole. 

The  same  effect  can  be  produced  by  means  of  the  electric  arc. 
By  connecting  the  positive  pole  of  a  generator  with  the  hearth 


246  Blast  Furnace. 

jacket  and  applying  the  negative  pole  connection  in  the  shape  of 
xi1;  ?>!'«£.'  a  large  carbon  to  the  tapping  hole,  an  arc  may  be  established  that 
will  readily  melt  obstructions.  To  obtain  satisfactory  results, 
however,  the  current  should  not  be  less  than  400  amperes,  at  220 
volts  pressure.  It  is  still  better  to  have  1,000  amperes,  at  no 
volts,  when  the  action  is  said  to  be  more  rapid  than  the  oil  blow 
pipe.  It  is  necessary,  however,  to  protect  the  eyes  with  heavily 
smoked  glasses,  as  the  rays  from  the  arc  produce  after  effects 
which  incapacitate  the  unprotected  beholder  for  a  day  or  two. 

A  still  more  recent  method,  known  as  the  Menne  process, 
consists  of  burning  the  iron  itself  by  means  of  compressed 
oxygen.  The  apparatus  consists  of  an  ordinary  oxyhydrogen  or 
May  IT,  1906!  hydrocarbon  blowpipe  with  a  long  nozzle,  by  which  the  tempera- 
ture of  the  point  to  be  attacked  is  raised  to  incandescence.  The 
supply  of  fuel  is  then  shut  off,  and  the  oxygen  alone  played 
against  the  heated  metal  at  a  pressure  of  30  atmospheres.  The 
heat  developed  by  the  oxidation  of  the  metallic  iron  and  the  metal- 
loids is  sufficient  to  render  the  resulting  oxides  into  a  thoroughly 
fluid  condition  and  the  pressure  of  the  oxygen  blast  keeps  the 
hole  clear.  A  higher  temperature  can  be  obtained  from  the  burn- 
ing metal  than  from  the  hydrogen,  as  the  volume  is  so  much  less 
that  the  heat  is  better  concentrated.  It  is  said  that  this  method 
can  penetrate  nearly  a  foot  of  metal  per  minute.  It  is  manifestly 
useless,  however,  when  slag  forms  the  obstruction,  since  its  very 
existence  depends  on  an  oxidizable  obstruction. 

When  a  large  quantity  of  scaffold  material  falls  into  the 
hearth,  it  not  only  chills  the  tapping  hole,  but  frequently  the 
cinder  notch  as  well.  At  the  same  time,  it  usually  forces  molten 
iron  and  cinder  up  around  and  into  the  tuyeres,  where  they  chill. 
It  is  not  uncommon,  therefore,  to  have  every  opening  into  the 
lower  part  of  the  furnace  chilled  up  tight.  Under  such  circum- 
stances it  is  impossible  to  keep  the  blast  on  the  furnace,  since 
the  tuyeres  are  closed.  It  is  necessary  then  to  open  them  by  an 
auxiliary  means  of  melting,  and  get  the  blast  on  as  soon  as 
possible.  This  is  best  done  by  attacking  two  or  three  points  at 
once,  such  as  the  cinder  notch  and  an  adjacent  tuyere  or  both 
adjacent  tuyeres.  This  will  soon  create  ingress  for  blast  at  two 
tuyeres  and  provide  an  outlet  for  molten  products  as  fast  as  made. 


Furnace  Irregularities.  247 

The  other  tuyeres  may  be  recovered  in  succession  while  the 
cinder-notch  serves  as  outlet  for  both  cinder  and  iron.  Oil  fed 
into  the  belly  pipes  will  act  as  a  blow  pipe  until  good  fuel  again 
appears  at  the  tuyeres.  When  melting  has  been  restored,  a  coke 
blank  should  be  charged,  and  then  an  outlet  through  the  tapping- 
hole  made  by  the  blow  pipe.  By  means  of  internal  and  external 
combustion  the  hearth  can  be  gradually  restored  to  normal 
condition. 


CHAPTER   VII. 

HINTS  ON  DESIGN  AND  EQUIPMENT. 
FURNACE    DESIGN. 

In  the  construction  of  plants  for  producing  pig  iron,  experi- 
ence has  shown  that  practically  any  expense  is  justifiable  that 
leads  to  material  economy  of  operation.  There  are  three  cardinal 
points  in  economical  operation  that  may  depend  directly  upon 
plant  design,  first,  large  output,  second,  low  fuel  consumption, 
and  third,  low  cost  of  handling  materials  and  products. 

The  output  of  a  furnace  plant  may  be  considered  as  dependent 
upon  two  chief  factors — viz.,  the  size  of  the  furnace  hearth  and 
the  capacity  of  the  blowing  equipment. 

The  fuel  consumption  will  depend  upon  the  furnace  lines  and 
the  heating  capacity  of  the  stoves. 

The  cost  of  handling  materials  and  products  will  depend  upon 
the  design  of  the  stock  handling  arrangements  and  the  systems 
of  handling  iron  and  slag. 

Size  of  Hearth. — The  keynote  of  every  furnace  plant  is  its 
output.  The  dominating  factor  in  the  question  of  output  is  the 
size  of  the  furnace  hearth.  The  rate  of  smelting  must  always 
be  in  proportion  to  the  rate  of  fuel  combustion.  The  rate  of  com- 
bustion under  given  conditions  is  tolerably  constant  per  square 
foot  of  hearth.  The  output  must,  therefore,  depend  largely  upon 
the  hearth  area.  It  is  true  that  the  nature  of  the  ore,  the  kind 
of  fuel  and  the  quality  of  product  all  have  a  bearing  upon  the  rate 
of  smelting;  but  with  average  mixtures  of  ores  and  average 
quality  of  coke  and  usual  forms  of  pig,  every  well-working  hearth 
should  consume  at  least  6000  pounds  of  coke  per  square  foot  in  24 
hours.  With  this  assumption  as  a  basis,  the  hearth  area  for  any 
output  at  a  given  fuel  consumption  may  be  figured.  For  example, 
a  furnace  to  make  400  tons  of  iron  in  24  hours  in  a  fuel  consump- 
tion of  2240  pounds,  would  require  a  hearth  area  of  - 
150  square  feet,  or  a  diameter  of  about  14  feet. 

248 


Hints  on  Design  and  Equipment.  249 

For  unusual  ore  or  fuel  conditions,  it  is  necessary  to  acquire 
experience  as  a  guide  to  the  especial  needs.  Charcoal,  because 
of  the  large  surface  which  it  presents  to  the  blast,  permits  a  more 
rapid  rate  of  combustion  than  coke,  and  hence  a  higher  duty  per 
square  foot  of  hearth  area.  On  the  other  hand,  the  substitution 
of  anthracite  coal  for  coke  would  not  permit  more  than  half  the 
full  estimated  production  of  the  hearth. 

The  hearth  area  should  be  adapted  to  the  kind  of  iron  to  be 
made.  Small  hearths  are  better  suited  to  making  foundry  irons, 
because  they  concentrate  the  heat  and  reducing  conditions  and  Jg^ 
thereby  produce  higher  silicon  content.  At  the  same  time,  how- 
ever, the  higher  fuel  ratio  demanded  by  foundry  irons  decreases 
the  duty  per  square  foot  of  hearth  area  and  a  lower  output 
follows. 

The  crucible  capacity  should  be  about  3  cubic  feet  per  ton  of 
pig.     For  a  14  foot  hearth,  this  means  a  depth  of  about  8  feet. 
Since  each  ton  of  iron  occupies  5  cubic  feet  of  space,  it  follows   xxxiv.f1' E*' 
that  if  the  furnace  is  to  be  tapped  every  six  hours,  the  well  below   p'608' 
the  cinder  notch  must  have  a  depth  of  at  least  3^  feet.    If  tapping 
occurs  oftener,  a  lesser  depth  may  suffice,  but  is  not  advisable. 

Bosh. — When  the  size  of  the  furnace  hearth  has  been  de- 
cided upon,  every  other  dimension  should  be  brought  into  har- 
monious proportion.  The  most  successful  of  the  modern  furnaces 
have  bosh  areas  two  to  two  and  a  half  times  that  of  the  hearth. 
A  hearth  of  14  feet  diameter  would  therefore  require  a  bosh  area 
of  300  to  375  square  feet,  which  corresponds  to  diameters  of  20  to 
22  feet.  If  we  take  21  feet  diameter  as  the  size  of  the  bosh,  a 
bosh  angle  of  75  degrees  from  the  horizontal  would  bring  the  bosh 
at  a  height  of  about  13  feet  above  the  top  of  the  crucible. 

The  bosh  angles  best  suited  to  different  materials  can  be  deter- 
mined only  by  experience.  The  usual  slope  to-day  is  from  70  to 
80  degrees,  with  best  results  at  about  75  degrees.  Less  than  70 
degrees  slope  is  so  flat  that  it  permits  accumulations  which  slip 
periodically,  causing  irregular  work.  More  than  80  degrees  is 
likely  to  bring  the  bosh  above  the  zone  of  fusion  and  permit 
hanging. 

Shaft. — A  stockline  diameter  about  equal  to  that  of  the 
hearth  is  ample  for  all  purposes.  The  location  of  the  stockline  is 


250 


Blast  Furnace. 


r 


T 


1520   CU.  FT. 


11750    CU.  FT. 


TOTAL  VOLUME       17600  CU. FT 
WORKING  VOLUME  15000  CU. FT 


Lines  of  a  Modern  Blast  Furnace. 


Hints  on  Design  and  Equipment. 


251 


determined  by  the  position  and  drop  of  the  bell.  Usually  the  space 
occupied  by  the  hopper,  plus  the  drop  of  the  bell,  and  clearance 
below  it,  will  leave  at  least  10  feet  of  dead  space  between  the 
charging  platform  and  the  stockline.  For  an  80  foot  furnace  this 


5000  LBS.  COKE 
PER  SQ.    FT.  HEARTH  AREA 


6000  LBS.  COKE 
PER  SQ.  FT.  HEARTH  AREA 


7000  LBS.  COKE 
PER  SQ,  FT.  HEARTH  AREA 


-  ZONE   OF  HEAT    INTERCEPTION   IN  FEET 


\\\v 


_ 

X  Oi 


\ 


88 


FUEL  CONSUMPTION   IN  LtsS.  PER  TON-PIG 


Diagram    Showing   Relation   Between    the    Fuel   Consumption    and  Rate  of  Combustion  on 
the  One  Hand  and  the  Length  of  Heat  Intercepting  Zones  and  Rate     of  Travel  of  Stock 
on  the  Other,  at  Various  Fuel  Consumptions  and  Bosh  Ratios. 
(Full  Line  =  Bosh  2%  Times  Hearth  Area.) 
(Broken  Line  =  Bosh  2  Times  Hearth  Area.) 


would  leave  49  feet  as  the  distance  from  the  bosh  to  the  stockline. 
The  taper  from  21  to  14  feet  gives  the  inwalls  a  total  batter  in 
that  distance  of  42  inches  on  every  side,  which  is  equal  to  0.85 
inches  per  foot.  The  batter  varies  in  general  practice  from  ^  to 
I  inch  per  foot.  This  gives  a  total  volume  of  17,600  cubic  feet  or 


252  Blast  Furnace. 

44  cubic  feet  per  ton  of  iron  in  24  hours.     With  Lake  Superior 
ores  the  latter  volume  generally  ranges  from  30  to  50  cubic  feet. 

TABLE  SHOWING  AIR  REQUIREMENT,  OUTPUT  AND  LENGTH  OF  ZONE 
OF  HEAT  INTERCEPTION  FOR  VARIOUS  FUEL  CONSUMPTIONS 
AND  BOSH  RATIOS. 


Pounds  Cubic  Pounds 
coke       feet       of 
burned     air      iron     Gross 
per  sq.  per  sq.  per  sq.  tons  of 
ft.  of     ft.  of     ft.  of  iron  per 
hearth  hearth  hearth  sq.  ft. 
Fuel  con-            in  24      per      in  24     in  24 

Bosh  area  2% 
times  hearth  area. 
Time  of 
stock  in  furnace. 
12  h.    15  h.  18  h. 

Bosh  area  double 
hearth  area. 
Time  of 
stock  in  furnace. 
12  h.  15  h.    18  h. 

sumption.          hours,  minute 

.  hours. 

hours. 

Feet. 

Feet. 

Feet. 

Feet. 

Feet. 

Feet. 

r  5.000 

191 

5.600 

2.5 

39 

49 

59 

47 

58 

69 

2,000  Ib. 

per  ton  \  6,000 
[7,000 

229 
267 

6.720 

7,840 

3.0 
3.5 

47 
55 

59 
69 

71 

83 

55 
64 

69 

80 

83 
96 

fs.ooo 

191 

5,000 

2.232 

34.5 

43.2 

51.8 

40.3 

50.4 

60.5 

2,240  Ib. 

per  ton  \  6.000 

229 

6.000 

2.679 

42.0 

52.0 

62.0 

49.0 

<»<».."> 

73.0 

[7,000 

267 

7,000 

3.125 

48.3 

60.4 

72.5 

56.5 

70.6 

84.7 

f  5,000 

191 

4,480 

2.0 

30.4 

38.0 

45.6 

35.5 

44.3 

53.1 

2,500  Ib. 

per  ton  \  6.000 

229 

5,376 

2.4 

36.4 

45.5 

54.6 

42.5 

53.1 

63.7 

[7,000 

267 

6,272 

2.8 

42.6 

53.2 

63.9 

49.6 

62.0 

74.4 

FURNACE    CONSTRUCTION. 

Foundations.— The  foundation  of  a  blast  furnace  cannot  be 
too  solid.  It  should  reach  down  to  bedrock  or  hardpan,  and  below 
the  general  level  of  the  yard  may  consist  of  concrete.  Above  the 
yard  level,  however,  the  construction  should  be  of  brick.  For 
convenience  of  handling  the  product  in  ladles  or  cars  running  on 
the  general  yard  level,  it  is  always  desirable  to  have  the  hearth 
level  at  least  10  feet  above  the  yard  level.  The  construction  from 
the  yard  level  to  the  hearth  level  is  best  made  of  firebricks, 
although  red  bricks  may  be  substituted  outside  the  circle  marked 
by  the  hearth  jacket.  The  space  between  the  foundations  and  the 
cast  house  wall  should  be  filled  with  loose  material  in  order  to 
check  breakouts. 

Columns.— The  columns  which  support  the  mantle  are 
placed  upon  the  foundations  at  the  hearth  level.  The  columns 
may  be  cast  iron  or  may  be  built  up  of  structural  steel.  It  is 
difficult  to  get  cast  columns  with  metal  of  uniform  thickness  when 
more  than  18  feet  long,  and  as  recent  columns  are  sometimes  24 
feet,  there  is  a  tendency  to  use  built  up  columns.  It  is  convenient 
to  have  half  as  many  columns  as  tuyeres,  so  that  the  tuyeres  may 


--  >*.  *•«  Tfi  O  I-  00  O  01  CO  1C  I-     •— - 
M  •£  rH  rH  rH  rH  rH  O}  OJ  O)  O4  Ol    ,  X 


l?l 


a  a 

.2  a 
>o    . 


•*-*    I 

li 


V 


1C  1C  CO  CO  CO  CO 


H     — 


£  "8  5  •»  HI  £  S 

S  3  C  h    i  o  O 

°     Q,  '2  <V      I      rH    •* 

PQ 


"    0    rH    rH    rH    Ol    Ol    0' 


O    O    O    O 

CO    00^  C0_  Ci_ 


.sllllt 

**<  ^  V    \  £    C 

!§!"§ 


O    e   1C  000000  1C  00 

2     g    CO    I-    rH    1C    O    1C    rH    I-    Tji    rH 
M    £    rH    rH  .Ol    Ol    CO "CO    •*    ^    1C   CO 


•sllllPgg 

o  ?  §  -3. 1 1  2  1 1 


-  " 

OJ      r;     O1 

•a  so  <" 


o  o 

o  o 
o  o 


o  o  o  o 
o  o  o  o 

O   O   ©_  1C 

§'  O  O"  Of  I-  CO"  rH  r-T 
O  CO'  1C  I-  O  CO  CO 
rH  rH  rH  rH  Ol  Ol  O-l 


02 


IJ§f3l§ra 


^  "c  5  w  r  "S,  ^  co  co  ^  ic 

*•  O  <w     P    o  00 


a  £  .2  »  2  "I  »  ic  ic  ic  o  o  o  o  o  o  o 

B    «M    "S     g    5   5     M    rH'    OS    00    d    O    Oi    1C    O 
3     w    -.-1    T;    _u    r^    ~A    T«    10    I-    X    O    rH 


o   t^   -^   O   O 
s*  P  *-"  O  O 

OJ     C       •    CO   CO 


§0000 
o  o  o  o 

O   1C    "^    CO   Ol 


n    5    flOrH^^1-100'- 
— '     g     *"    w    rH    rH    rH    Ol    OI-CO   CO 


^*2 

^S 


«  5   a  S  'S   8     : 
_  h  1  o  2  5  C 


w        ^ 


,0000000000 

co  -Q   S     •  co  co  co  co  co  co  co  co  co  co 

fcH    o   ^     S   Ol   Ol   O4   Ol   Ol    Ol   Ol   Ol   Ol  .Ol 

.S   £  01  ° 


-|o 


p    OS          CO   CO   1C   O  O  b-;   O   t-;  O   O 

*     S     £   O    CO    GC    1C    CO   OJ    rfJ   CD    rH    t^ 
-H     b     OS    1C   CO    I-    C5    rH 


W   -     (J 
H   ^    - 


O    rH    OJ    CO 


254  Blast  Furnace. 

be  placed  symmetrically,  two  between  every  pair  of  columns.  The 
columns  support  the  mantle  and  are  bolted  at  the  bottom  to  heavy 
cast  iron  base  plates,  which  rest  on  the  foundations. 

Hearth. — The  crucible  jacket  may  be  iron  or  steel  castings 
made  in  segments  and  bolted  together,  or  it  may  consist  of  riveted 
steel  plate,  I  inch  or  more  in  thickness,  reinforced  by  heavy  bands. 
The  latter  construction  is  more  rigid  and  also  cheaper  than  the 
cast  segments.  The  jacket  should  be  set  well  into  the  foundation 
brickwork,  at  least  4  feet  below  the  hearth  level,  and  should  be 
cylindrical  in  shape.  Conical  jackets  tend  to  move  upward  during 
expansion,  and  any  movement  is  likely  to  permit  the  formation  of 
cracks  in  the  brickwork  which  may  lead  to  breakouts.  An  open- 
ing in  the  front  of  the  hearth  jacket  at  least  12  inches  wide  and 
30  inches  high  should  be  left  at  the  hearth  level  for  the  tapping 
hole.  It  should  be  surrounded  by  a  Z  bar  collar  to  shed  water. 

The  crucible  jacket  is  generally  cooled  to  pi  event  breakouts, 
and  the  system  of  cooling  is  modified  by  the  style  of  jacket.  Cast 
jackets  are  sometimes  so  heavy  that  the  mass  of  metal  acts  as  a 
chill.  Generally,  however,  they  are  cooled  by  water  flowing  in 
wrought  iron  pipes  enclosed  in  them  when  they  are  cast.  Some- 
times external  gutters  filled  with  flowing  water  are  used.  Riveted 
plate  jackets  may  be  cooled  by  sprays  of  water  directed  against 
the  external  surface,  or  by  internal  rows  of  vertical  wrought  iron 
pipes,  laid  either  against  the  jacket  or  incased  in  cast  iron.  Sur- 
face cooling  with  water  under  gravity  is  preferable  to  internal 
pipes,  which  requires  water  under  pressure,  because  the  latter  is 
difficult  to  manage  when  a  breakout  cuts  the  pipe. 

Cinder  Notch — The  cinder  notch  usually  comes  at  about  the 
top  of  the  crucible  jacket  to  which  the  cinder  runner  is  bolted. 
The  cinder  notch  usually  consists  of  three  pieces,  although  the 
intermediate  ring  is  sometimes  omitted.  The  water-cooled  parts 
are  usually  copper  or  bronze,  though  the  outer  cooler  is  often 
cast  iron  containing  a  coil  of  wrought  iron  pipe.  The  latter  is 
preferable  whenever  it  is  necessary  to  cast  through  the  cinder 
notch,  as  the  cast  iron  is  less  quickly  destroyed  by  molten  iron 
than  copper  or  bronze. 

Furnace    Level. — The  working  level  around  the  furnace  is 


Hints  on  Design  and  Equipment.  255 

usually  2  or  3  feet  above  the  hearth  level,  except  at  the  front, 
where  it  is  lower  to  give  access  to  the  tapping  hole.  With  surface 
cooling  of  the  hearth  jacket,  an  open  drain  4  inches  wide  called 
the  "  well  "  is  provided  in  the  brickwork  around  the  crucible  walls, 
to  allow  the  cooling  water  to  reach  the  bottom  of  the  jacket.  This 
drain  should  be  kept  full  of  gravel  or  other  porous  rilling,  which 
will  allow  free  drainage.  Formerly  it  was  customary  to  have 
wells  i  to  2  feet  wide  kept  full  of  water,  which  in  case  of  break- 
outs caused  disastrous  explosions  and  permitted  the  wells  to  fill 
with  iron. 

Tuyeres — The  crucible  wall  is  pierced  for  tuyeres,  so  that 
their  centres  are  18  to  24  inches  below  its  top,  which  allows  suffi- 
cient space  for  the  tuyere-breast  casting  below  the  flare  of  the 
bosh  wall.  In  the  case  under  supposition,  this  would  leave  about 
3  feet  between  the  cinder  notch  and  the  line  of  the  tuyeres.  Since 
the  bottom  of  the  tuyeres  marks  the  limit  to  which  cinder  should 
rise,  this  space  should  be  as  high  as  possible. 

The  number  of  tuyeres  used  for  a  given  size  of  hearth  varies 
widely,  although  there  is  a  tendency  to  come  to  the  uniform  rule 
of  a  tuyere  for  each  foot  of  hearth  diameter.  This  rule  gives  a 
uniform  distance  between  tuyere  centers  of  almost  exactly  3  feet. 

The  tuyere  should  not  be  so  small  that  it  will  throttle  the 
blast,  nor  so  large  that  the  blast  will  lack  penetration.  The  best 
results  have  been  attained  when  each  square  inch  of  tuyere 
opening  passes  about  100  cubic  feet  of  piston  displacement  per 
minute.  In  order  to  pass  35,000  cubic  feet  of  air  per  minute  at 
this  rate,  350  square  inches  will  be  required ;  14  tuyeres,  therefore, 
would  need  a  diameter  of  6  inches  each  in  the  clear. 

Tuyeres  are  sometimes  made  in  three  pieces  like  the  cinder 
notch,  but  as  a  rule  the  tuyere  and  cooler  alone  compose  the 
system.  The  average  projection  of  the  tuyere  beyond  the  nose 
of  the  cooler  is  about  6  inches,  which  seems  to  give  the  best 
results.  Less  projection  allows  the  combustion  to  attack  the  walls 
above  the  tuyeres.  More  projection  simply  reduces  the  working 
area  of  the  hearth.  Attempts  to  distribute  the  blast  horizontally  TV.  A.  i.  M.  E. 

*        XVI 1 1.,  p.  858. 

by  special  shapes  of  tuyere  nose  causes  cutting  of  walls  beside 
the  tuyeres. 

Copper  tuyeres  cost  somewhat  jnore  than  bronze,  but,  owing 


256  Blast  Furnace. 

to  their  better  conductivity,  they  resist  burning  better  and  stand 
abrasion  quite  as  well.  They  should  be  fed  at  the  bottom  by  a  i  % 
inch  pipe  and  the  outlet  should  be  reduced  to  ^4  inch  or  less. 
The  outlet  pipe  should  be  at  the  top  and  should  extend  well 
toward  the  nose.  This  secures  a  better  circulation  at  low  pres- 
sures. Fifteen  to  twenty-five  pounds  is  ample.  A  small  opening 
in  the  outlet  pipe  at  the  top  of  the  tuyere  base  allows  for  escape 
of  any  trapped  air. 

Bosh  Construction — The  bosh  construction  is,  in  the  major- 
ity of  cases,  brick  with  bronze  cooling  plates.  Since  they  offer 
but  little  resistance  to  outward  pressure,  they  must  be  reinforced 
by  heavy  iron  bands.  Bosh  plates  of  the  Scott  type  with  arched 
top,  and  sides  tapered  and  nose  curved  to  coincide  with 
the  curvature  of  the  wall  are  most  used.  They  ex- 
tend the  full  depth  of  the  wall,  and  are  kept  filled 
with  water  by  a  positive  circulation.  As  a  rule,  a 
number  are  connected  in  series,  so  that  the  discharge  from 
one  becomes  the  supply  of  the  next.  Usually  the  temperature  of 
the  water  does  not  rise  more  than  10  to  20  degrees  F.  in  passing 
through  a  plate,  so  that  125  degrees  F.  is  a  perfectly  safe  limit 
for  inlet  water.  The  space  between  plates  horizontally  is  usually 
one  brick,  4^/2  inches,  so  that  the  proportion  of  the  plates  to  the 
circumference  is  75  to  85  per  cent.,  according  to  the  size  of  plate 
used.  Small  sizes  are  preferred.  Usually  they  are  spaced  ver- 
tically 12  to  24  inches  apart.  Hence  a  21  foot  bosh  13  feet  deep 
will  require  about  350  small  plates.  Above  the  bosh,  the  lower 
part  of  the  inwall  is  generally  protected  by  two  or  three  rows 
of  cast  iron  cooling  plates  or  coils  of  pipe  set  in  the  brickwork. 

Equally  good  for  small  furnaces,  and  probably  as  good  for 
any  size,  is  the  steel  plate  shell  construction  with  surface  cooling. 
It  is  a  stronger  form  "of  structure  than  bricks  reinforced  by  bands, 
and  much  less  expensive  than  a  multitude  of  bronze  bosh  plates. 
Furthermore,  only  about  one-third  the  quantity  of  bricks  is  needed 
for  lining,  since  a  9  inch  or  13  inch  wall  suffices.  A  segmental 
cast  bosh  jacket  with  troughs  or  pipe  circulation  is  still  in  use  in 
some  districts. 

Furnace  Shell — The  shell  of  the  furnace  shaft  is  always  of 
riveted  plate-construction  and  is  supported  by  a  mantle  which  is 


Hints  on  Design  and  Equipment. 


257 


Section   of  the  Eliza  Furnace. 


258  Blast  Furnace. 

bolted  to  the  top  of  the  columns.  The  mantle  is  sometimes  a 
segmental  cast  iron  ring,  but  now  is  more  usually  built  up  of  plates 
and  shapes.  The  furnace  shell  usually  has  a  taper  conformable 
to  the  batter  of  the  imvalls.  Near  the  top  it  is  pierced  for  the 
downtake  openings,  and  frequently  also  for  a  row  of  explosion 
doors,  whose  combined  area  may  be  one-half  the  area  at  the  stock- 
line.  The  explosion  doofs,  however,  do  not  appear  to  be  necessary 
as  the  so-called  "  top  explosions  "  are  not  due  to  increase  of  the 
volume  of  the  gases,  but  rather  to  their  inertia  of  motion  on 
sudden  release  from  obstructions.  In  order  that  the  gases  may 
not  carry  away  too  much  ore  as  flue  dirt  their  rate  of  escape 
through  the  downtake  should  not  exceed  32  feet  per  second.  For 
a  'gas  volume  of  1460  cubic  feet  per  second  at  450  degrees  F.,  re- 
sulting from  35,000  cubic  feet  of  blast  per  minute,  a  downtake  at 
least  7  feet  in  the  clear  is  necessary.  This  would  mean  one  open- 
ing of  7  feet  m  diameter,  or  two  of  5  feet,  or  three  of  4  feet,  or 
four  of  3l/2  feet. 

Furnace  Top The  furnace  "top  is  closed  with  a  bell  and 

hopper  so  designed  that  the  bell  has  2  to  2.y2  feet  clearance  all 
round  it  at  the  stockline.  The  hopper  should  have  an  available 
capacity  sufficient  to  hold  all  of  the  coke  needed  for  one  charge. 
The  use  of  a  second  bell  above  acts  as  a  seal  and  saves  the  waste 
of  gas  incident  to  dropping  the  charge.  The  systems  of  distribu- 
tion, which  provide  for  the  rotation  of  stock,  appear  to  give  best 
results. 

For  rilling  the  furance  two  balanced  skips  travelling  on  parallel 
tracks  work  best.  The  size  of  skip  should  be  in  accordance  with 
the  character  of  stock  and  rate  of  travel  of  the  skip.  Ordinarily 
the  stock  necessary  to  make  100  pounds  of  pig  occupies  5  to  $l/>, 
cubic  feet  of  space.  A  furnace  which  makes  400  tons  of  pig 
iron  in  a  day  must  make  640  pounds  per  minute  and  hence  use  30 
to  35  cubic  feet  of  stock  in  that  period. 

Stock  House — In  order  to  supply  the  skips  with  stock 
promptly  and  economically  it  is  necessary  to  have  proper  stock 
house  arrangements.  The  most  approved  method  consists  of  a 
series  of  bins  for  ore  and  stone,  ranged  generally  at  right  angles 
to  the  skipway,  and  served  by  an  electric  larry,  which  weighs  the 
stock  and  conveys  it  to  the  skip.  The  coke  bins  are  placed  on 


Hints  on  Design  and  Equipment.  259 

either  side  of  the  skip  so  that  the  coke  may  be  drawn  directly  into 
the  skip  and  charged  by  volume  instead  of  by  weight.  The 
arrangements  for  the  ore  and  stone  consist  either  of  a  series  of 
bins,  surmounted  by  an  elevated  track,  or  a  floor  provided  with  a 
row  of  chutes  leading  to  a  tunnel  beneath.  The  latter  arrangement 
is  less  subject  to  freezing  and  is  equally  adapted  to  hand  charging. 

For  storing  ore  for  future  use,  it  has  been  customary  to  use 
continguous  space  served  by  devices  for  economical  rehandling  of 
the  stock  in  bringing  it  to  the  stock  house.  There  is  a  recent  ten- 
dency, however,  to  put  the  storage  yard  near  the  hoist  and  have 
it  all  served  by  the  larry,  thereby  entirely  obviating  the  necessity 
of  rehandling. 

The  space  occupied  by  stock  when  thrown  loosely  in  bins  is 
usually  about  as  follows: 

Lake    ores 150  pounds  occupy  1  cubic  foot  space. 

Stone    100  pounds  occupy  1  cubic  foot  space. 

Coke    28  pounds  occupy  1  cubic  foot  space. 

The  bin  capacity  required  by  a  400  ton  furnace  will  evidently 
be  as  follows: 

400  X  2,240  X  1.7 

Ore  : —  =  10,000  cubic  feet  per  24  hours,  or  25  cu.  ft.  per  ton  pig. 

150 

400  X  3,120 
Stone:  —  —  =  4,480  cubic  feet  per  24  hours,  or  11  cubic  feet  per  ton  pig. 

100 

400  X  2,240 
Coke  :  -  —  =  32,000  cubic  feet  per  24  hours,  or  80  cubic  feet  per  ton  pig. 

Furnace  Linings. — A  considerable  factor  in  the  economy  of 
operation  of  a  blast  furnace  is  the  lengths  of  the  blasts.  The 
lengths  of  the  blasts  in  turn  are  largely  dependent  upon  the  quality 
of  the  furnace  lining. 

Furnace  linings  are  always  made  of  firebricks.  The  character 
of  the  bricks  needed  differs  in  different  parts  of  the  furnace.  As  a 
rule  three  kinds  are  used.  The  most  refractory  are  needed  for 
the  hearth  and  bosh  walls.  Those  forming  the  inwalls  should  be 
dense  to  stand  the  wear  of  descending  materials  and  resist  the 
action  of  the  gases.  The  top  bricks  which  receive  the  shock  of 
the  material  as  it  slides  off  the  bell  should  offer  infinite  resistance 
to  abrasion. 

All  firebricks  have  fireclay  as  their  basis.    Fireclay  is  a  hydrous 


260  Blast  Furnace. 

silicate  of  alumina,  resulting  from  the  decomposition  of  the  feld- 
spars which  occur  in  granites,  porphyries  and  other  igneous  rocks. 
During  the  decomposition,  the  feldspars  break  up  into  silicates  of 
alumina  and  the  alkalis.  The  latter,  being  readily  soluble,  are 
leached  out  by  circulating  underground  waters,  leaving  behind  the 
clay,  mingled  with  other  components  of  the  parent  rock,  such  as 
quartz,  mica  and  often  some  undecomposed  feldspar.  Pure  clays 
have  the  following  approximate  composition : 

SiO2    47  per  cent. 

AloO3    40  per  cent. 

H^O    13  per  cent. 

and  any  considerable  variation  from  these  proportions  indicates 
impurities  which  are  not  essential  to  the  substance. 

Fireclay  has  two  properties  which  render  it  valuable  in  the 
manufacture  of  refractories,  namely,  plasticity  and  refractoriness. 
Plasticity  is  a  quality  inherent  in  clay  and  peculiar  to  it.  It  is 
essential  to  the  shaping  and  the  persistance  of  shape  of  refractory 
articles.  It  is  impaired  by  the  presence  of  any  non-plastic  sub- 
stances, such  as  quartz,  mica,  feldspar,  limestone,  oxides  of  iron, 
etc.,  and  is  also  affected  by  high  temperatures,  excessive  pressure 
or  any  cause  which  decreases  the  normal  proportion  of  combined 
water. 

The  quality  of  refractoriness  depends  upon  both  the  chemical 
composition  and  the  physical  condition.  An  increase  in  percentage 
of  Al.jO3  or  of  both  SiO2  and  A12O,  as  in  calcination,  tends  to  make 
clay  more  refractory.  The  coarser  the  particles  and  the  less  in- 
timately mixed,  the  less  ready  the  fusibility.  By  mixing  calcined 
and  uncalcined  clays  and  non-plastic  refractory  materials  of  vari- 
ous degrees  of  coarseness,  bricks  of  almost  any  degree  of  density 
and  refractoriness  may  be  obtained.  Excellence  in  firebricks  de- 
pends upon  several  factors,  especially  proper  grinding,  bonding 
and  burning. 

Hearth  and  bosh  bricks  should  be  made  of  the  most  refractory 
clays  without  much  bonding  or  excessive  burning,  since  they  are 
subjected  to  heat  only.  The  coarser  the  material  the  less  readily 
will  it  be  fused.  Inwall  bricks  should  be  more  dense  than  bosh 
bricks  and  hence  should  be  more  finely  ground  and  more  thor- 
oughly burned.  Fine  grinding  and  burning  at  a  temperature  of 


Hints  on  Design  and  Equipment.  261 

2600  degrees  F.  usually  insures  sufficient  density.  Hearth,  bosh 
and  inwall  bricks  should  contain  less  than  2.]/2  per  cent,  oxide  of 
iron.  Top  bricks  may  contain  more  plastic  clay  than  inwall 
bricks.  They  should  also  be  finely  ground  and  well  burned.  They 
are  less  refractory,  but  this  is  partially  compensated  by  their  be- 
coming vitrified  during  burning.  Hardness  and  density  are  more 
important  than  refractoriness.  Well  burned  bricks  will  ring  when 
struck. 

In  selecting  bricks  for  lining  a  furnace,  it  is  important  to 
choose  those  which  are  suited  to  the  requirements.  Neglect  of 
this  precaution  is  a  leading  cause  of  unsatisfactory  results.  Soft, 
porous,  refractory  bricks  should  be  confined  to  the  hotter  parts  of 
the  furnace,  and  never  used  where  materials  are  still  solid.  Hard, 
strong  bricks,  which  contain  a  high  percentage  of  plastic  clay  are 
seldom  refractory,  and  therefore  should  be  used  for  no  higher 
temperatures  than  that  of  the  inwalls.  Bricks  should  be  uniform 
in  size  and  regular  in  shape  to  insure  good  joints  without  the 
use  of  much  mortar. 

In  laying  the  bricks  of  a  furnace  lining  it  is  usual  to  leave  a 
space  between  the  shell  and  the  lining  for  expansion.  This  space 
may  be  3  to  4  inches  wide,  and  is  usually  filled  in  with  yielding 
material  such  as  slagwool,  granulated  slag  or  loam  and  slag. 
Allowance  should  be  made  for  vertical  expansion,  also.  If  the 
ironwork  on  top  is  not  loose,  at  least  6  inches  should  be  allowed 
in  the  lining  of  a  furnace  80  feet  in  height. 

In  laying  firebricks,  lime  mortar  should  never  be  used,  as  at 
high  temperatures  the  CaO  would  attack  the  SiO2,  and  A12O3  of 
the  clay.  Firebricks  should  always  be  laid  in  a  slurry  of  fireclay 
and  water,  too  thin  to  be  handled  on  a  trowel.  The  bricks  should 
be  dipped  in  the  fireclay  and  laid  on  the  wall  and  hammered  close 
to  squeeze  out  all  of  the  fireclay  possible.  Any  excess  beyond  that 
necessary  to  fill  the  slight  inequalities  of  the  bricks  may  result  in 
shrinkage  cracks  on  drying.  The  top  of  each  course  should  be 
slushed  with  a  dipperful  of  the  slurry. 

STOVE  DESIGN. 

Since  stoves  are  intended  to  heat  the  blast,  it  follows  that  they 
should  be  in  proportion  to  the  blast  volume,  and  hence  should  bear 


262  Blast  Furnace. 

a  definite  relation  to  the  size  of  the  furnace.  They  should  be 
designed  for  a  given  volume  of  blast  at  a  definite  temperature.  In 
attaining  this  end  two  factors  must  be  considered — viz.,  the 
volume  of  bricks  and  the  area  of  surface  presented  to  the  blast. 
Since  it  is  undesirable  that  the  blast  temperature  should  vary 
materially,  the  weight  of  brick  should  be  such  that  it  can  give 
out  heat  continuously  for  an  hour  without  dropping  more  than 
100  degrees  F.  in  temperature.  As  the  blast  volume  is  usually 
three  or  four  times  that  of  the  checker  flue,  it  follows  that  a  given 
particle  of  air  is  in  the  stove  for  only  15  or  20  seconds,  and  that 
therefore  the  heating  surface  must  be  ample  to  communicate  its 
heat  rapidly. 

The  duty  of  a  stove  per  hour  is  evidently  equal  to  the  amount 
of  heat  carried  in  the  blast  per  hour.  In  the  case  under  considera- 
tion the  furnace  requires  about  35,000  cubic  feet  of  air  per 
minute,  which  equals  2672  pounds,  or  about  160,300  pounds  per 
hour.  The  heat  carried  in  this  quantity  of  blast  may  be  found  by 
the  formula, 

360,300  [0.2335   (t  —  t1)  +  0.0000208   (t2  —  f'2)],  where 
t  —  1,200  degrees  F.,  the  temperature  of  the  blast,  and 
t1  —  100  degrees  F.,  the  temperature  of  the  air. 

This  reduces  to  160,300  X  296  —  46,000,000  B.  T.  U.,  which  is 
the  amount  of  heat  to  be  furnished  per  hour  by  the  brickwork. 
Allowance  of  10  per  cent.  for.  losses,  will  bring  this  figure  up  to 
about  50,000,000  B.  T.  U.  If  this  is  to  be  accomplished  with  the 
loss  of  100  degrees  F.,  the  quantity  of  bricks  is  easily  calculated. 
The  heat  capacity  of  brick  is  about  0.2  B.  T.  U.  per  pound  per 
degree  F.  In  dropping  100  degrees  F.  they  will  yield 

0.2  X  100  =  20  B.  T.  U.  per  pound  of  brick. 

50.000,000  r  i    •  i 

—  =  2,500,000  pounds  of  brickwork. 

Assuming  that  a  9-inch  fireclay  brick  weighs  8  pounds,  and  that 
17  make  a  cubic  foot  of  solid  brickwork,  then  each  cubic  foot  will 
weigh  135  pounds.  Hence,  18,500  cubic  feet  or  about  315,000 
9-inch  bricks  are  needed  in  each  stove  to  furnish  blast  with  a  drop 
not  exceeding  100  degrees  F.  per  hour.  This  equals  nine  bricks 
per  cubic  foot  of  blast  per  minute,  or  about  */2  cubic  foot  of  brick- 
work per  stove  for  each  cubic  foot  of  blast. 


Hints  on  Design  and  Equipment.  263 

The  cross  section  of  a  stove  having  a  checkerwork  60  per  cent, 
bricks  and  40  per  cent  flues  would  represent  a  total  volume  equal  to 

18,500  X  ioo 

— 7— —          -  31,000  cubic  feet  of  checkers  per  stove. 

A  stove  22  feet  in  diameter  has  an  area  of  380  square  feet. 
Therefore  the  checkers  must  have  a  height  of, 

31,000 

'    =  82  feet. 
380 

About  12  feet  more  are  required  for  the  dome,  making  a  total 
height  of  the  stove  at  least  95  feet.  Since  1000  checker  bricks 
will  yield  about  140  square  feet  of  heating  surface,  the  total 
heating  surface  per  stove  will  approximate  44,000  square  feet. 
For  four  stoves  this  will  equal  176,000  square  feet,  or  about  5 
square  feet  per  cubic  foot  of  blast  per  minute,  which  practice 
shows  to  be  ample. 

TABLE   OF    RELATIVE   PROPORTIONS   OF   SOME   OF   THE    CHIEF    MAKES 
OF    HOT   BLAST   STOVES    USED    IN    THIS    COUNTRY. 

II  II   ^   !li!lll!ll1l^li    II  111 


5:3a;a>oi:*-'3aj(i'-£<5.24'-Msb1  &"?       <u  £ 

o~    *a     gfe,      45*  |£'««*|M*-g-fia      g»    32,5 

Foote    Side.  2  22x300  43  110  2.7  41.8  54,000  352,000  153 

Kennedy    Central.  2  22x100  3.~>  118  3-4  40.3  47,000  362,000  130 

McClure Central.  3  22x100  33  J  24  3.7  41.3  52,000  395,000  132 

Roberts Side  2  22x100  47  84  1.8  34.S  39,700  360,000  110 

Stove  Efficiency — The  quantity  of  gas  required  by  the  stoves 
and  the  maximum  temperature  obtainable  may  be  determined 
from  the  above  conditions.  The  gases  which  escape  from  the  fur- 
nace have  the  following  composition  per  pound : 

CO    0.2384  pound.  II, 0.0005  pound. 

C02    .  . , 0.1803  pound.  H2O    0.0311  pound. 

N2    0.5437  pound. 

1.0000  pound. 

At  a  temperature  of  450  degrees  F.,  the  quantity  of  heat  ex- 
isting in  the  gases  per  pound  if  cooled  down  to  60  degrees  F.  'may 
be  found  as  follows;  when  t—t'  —  390,  and  tz—t'2  =  198,900; 


f>64  Blast  Furnace. 

B.  T.  u. 

CO  0.2384  [(0.2405  X  390)  +  (0.00002143  X  1DS,900)]  =  0.2384  X 

98.057  — 23.37<i 

CO2  0.1863  [(0.1S7  X  390)  4-  (0.000111  X  l'.»s.9;i:>j  |  =  0.1SG3  X  95.008  =17.700 
N2  0.5437  [(0.2405  X  390)  4-  (0.00002143  X  198,900)]  =  0.5437  X 

98.057  =  53.313 

II2  0.0005  [(3.367  X  390)   +   (0.0003  X  198,900)]   =  0.0005   X  1371.80  =    0.683 
HoO  0.0311  [(0.42X390)  +  (0.000185  x  198,900)]  =  0.0311  X  200.496  =    6.2S5 


Sensible  heat  available  in  gases  per  pound  = 101.310 

Allowing  10  per  cent,  to  be  lost  by  cooling  through  radiation 
from  downtakes,  distributing  pipes  and  burners,  we  may  realize 
about  90  B.  T.  U.  of  sensible  heat  per  pound  of  gas. 

If  the  CO  and  H2  burn  to  CO2  and  H2O,  respectively,  in  the 
presence  of  50  per  cent,  excess  of  air,  then  the  amount  of  heat 

developed  per  pound  of  gas  will  be, 

B.  T.  u. 

per  pound. 

(0.2384  X  4,325)  -f   (0.0005  X  51,700)  = 1,057 

Adding  the  sensible  heat  of  the  gases  = 90 

We  have 1,147 

as  the  total  quantity  of  actual  and  potential  heat  per  pound  of 
gases. 

Assuming  that  the  waste  products  of  the  combustion  pass  out 
of  the  stoves  at  a  temperature  of  600  degrees  F.,  we  may  deter- 
mine the  amount  of  heat  lost  in  the  escaping  gases.  The  final 
products  of  the  combustion  may  be  found  as  follows: 

Net  air  needed 

Composition  of  gases  per  pound       for  combustion.  Products  of  combustion, 

air  and  changes  they  undergo.         O2                N».  CO2.  N2.  H2O. 

0.2384  CO  to  CO2  requires 0.13G2          0.4495  0.3746  0.4495              

0.1863    CO2.. ' 0.1863  

0.5437  No 0.5437              

0.0005  H2  to  H2O  requires 0.0040          0.0132             0.0132  0.0045 

0.0311    H2O 0.0311 


1.0000  0.1402          0.4627          0.5609          1.0064          0.0356 

The  air  needed  for  combustion,  0.1402  +  0.4627  --.  0.6029  pounds, 
whence  50  per  cent,  excess  equals  0.3015  pounds. 

The  total  available  heat  carried  away  at  600  degrees  P.  may  now  be  found  as 
follows  :  When  t  —  tl  =  540  and  t-  —  f  2  =  356,400. 

B.  T.  U. 

CO2  0.5609  [(0.187  X  540)  +  (0.000111  v  356,400)]  =  0.5609  X  140.54  =  78.83 
N2  1.0064  [  (0.2405-  X  540)  +  (0.00002143  X  356,400)]  =  1.0064  X 

137.51  =  138.40 

H2O  0.0356  [1.0.42  X  540)  +  (0.000185  X  356,400)]  =  0.0356  X  292.73  =  10.42 
Air    0.3015   [(0.2335   X  540)  -f  (0.0000208  X  356,400)]  =0.3015  X  133.50=  40.25 

1.9044 
Total  available  heat  lost  in  products  of  combustion  escaping  at  600°  =  267.90 


Hints  on  Design  and  Equipment.  965 

From  this  it  appears  that 

267.9  X   ioo 

-  =   23.4  per  cent. 
1147 

of  the  heat  available  in  the  furnace  gases.  Assuming  10  per  cent, 
additional  to  cover  losses  due  to  radiation,  etc.,  the  net  efficiency 
of  the  stoves  under  these  conditions  cannot  be  far  from  75  per 
cent.,  and  the  net  effective  heat  per  pound  of  gas  is 

1147  X  75  =  about  860  B.  T.  U. 
ioo 

Gas  Requirement — To  furnish    the  heat  for    the  blast  for 

50,000,000 
one  hour  requires,   -  — ^ =  58,150  pounds  of  gas  per  hour. 

oOO 

The  total  gas  made  per  hour  by  a  furnace  making  400  tons  of 
iron  per  day  on  2240  pounds  of  fuel  will  be  571.2  X  373^3  = 
213,250  pounds.  The  quantity  of  gas  required  by  the  stoves  is 

evidently,  — -   =  27  per  cent,  of  the  total  gas  formed. 

213,250 

On  a  fuel  consumption  of  2500  pounds,  this  requirement  falls 
nearly  to  25  per  cent.,  but  with  2000  pounds  it  rises  to  29  per 
cent,  of  the  gas  made.  The  consumption  of  25  per  cent,  of  the 
gas  on  a  fuel  consumption  of  2240,  on  the  other  hand,  would  per- 
mit a  blast  temperature  of  only  about  noo  degrees  F.,  instead 
of  1 200  degrees  F.,  but  at  the  same  time  the  volume  of  brick- 
work could  be  reduced  from  18,500  cubic  feet  to  15,200,  which 
requires  only  about  260,000  9-inch  bricks. 

Ordinarily  I  square  inch  of  gas  burner  area  is  sufficient  for 
^200  square  feet  of  stove  heating  surface. 

Stove  Linings. — In  lining  the  stoves  the  firebricks  should 
be  preceded  by  a  layer  of  cement  on  the  bottom  to  exclude  mois- 
ture completely.  Between  the  shell  and  the  first  row  of  bricks 
an  expansion  space  of  2  to  2T/2  inches  should  be  left  from  bottom 
to  top.  This  space  may  be  filled  with  slagwool  or  other  loose 
material  except  at  the  bottom,  where  cement  should  be  used.  The 
temperature  at  the  bottom  is  never  high  enough  to  cause  much 
expansion,  and  the  cement  will  prevent  leakage  if  the  lower  plate 
rusts. 

Stove  bricks  are  not  subjected  to  such  severe  temperature  as 
hearth  and  bosh  bricks,  hence  are  not  so  refractory,  nor  should 


266  Blast  Furnace. 

they  be  as  hard  as  inwall  bricks.  They  must  be  capable  of  with- 
standing changes  in  temperature  without  cracking,  and  of  resist- 
ing the  disintegrating  action  of  gases,  and  must  possess  porosity 
sufficient  to  absorb  and  give  out  heat  readily.  Glazed  or  vitrified 
bricks  do  not  take  up  heat  rapidly,  hence  vitrification  should  be 
avoided.  But  it  is  desirable  that  the  temperature  of  burning 
should  be  high  enough  to  convert  all  of  the  iron  oxides  present 
in  the  clay  into  silicates,  so  that  they  may  not  be  disintegrated  by 
the  gases.  A  tolerably  refractory  brick  should  be  used  for  the 
combustion  chamber,  or  it  may  become  vitrified.  For  hot  blast 
mains  and  gas  flues  a  less  refractory  brick  may  be  used.  A  dense, 
hard  brick  is  desirable  whenever  the  gases  carry  much  dust,  such 
as  in  the  downtake  and  gas  flues. 

Bustle  Pipe. — The  blast  connections  should  be  of  such  ca- 
pacity that  there  will  be  no  throttling  of  the  blast,  or  excessive 
loss  of  head  due  to  friction.  For  this  reason,  the  smallest  area 
of  the  bustle  pipe  should  never  be  less  than  the  combined  area 
of  the  tuyere  openings,  or  350  square  inches,  which  is  equivalent 
to  21  inches  diameter  in  the  clear.  Allowance  for  a  9-inch  lining 
would  require  a  pipe  at  least  40  inches  in  diameter. 

Blast  Mains. — As  regards  the  hot  and  cold  blast  mains,  a 
suitable  diameter  may  be  approximated  when  the  length  and  per- 
missable  loss  in  friction  have  been  determined. 

If  we  assume,  for  example,  a  hot  blast  main,  whose  average 
length  from  bustle  pipe  to  stove  is  100  feet,  and  a  cold  blast  main 
whose  average  length  from  stoves  to  engine  is  150  feet  and  that 
the  temperature  of  the  air  in  each  is  1200  degrees  F.  and  150 
degrees  F.,  respectively,  at  15  pounds  pressure,  we  may  calculate 
approximately  the  area  of  pipe  desirable  to  deliver  35,000  cubic- 
feet  piston  displacement  per  minute. 

Air  at  60  degrees  P.  and  atmosphere  pressure  weighs  0.076  pound  per  cubic  foot. 
Air  at  150  degrees  F.  and  15  pounds  pressure  weighs  0.130  pound  per  cubic  foot. 
Air  at  1,200  degrees  F.  and  15  pounds  pressure  weighs  0.048  pound  per  cubic  foot. 
Whence  it  appears  that  the  engine  delivers 
35,000 

=  583  cubic  feet  per  second. 

60 

0.076 
And  the  cold  main  transmits  583  X  -    -  =  340  cubic  feet  per  second. 

0.130 
0.076 

And  the  hot  main  transmits  583  X =  923  cubic  feet  per  second. 

0.048 


Hints  on  Design  and  Equipment.  267 

If  we  assume  further,  for  example,  that  the  total  drop  in 
pressure  between  the  engines  and  the  bustle  pipe  must  not  exceed 
i  pound,  of  which  3  ounces  may  take  place  in  the  stove,  3  ounces 
in  the  cold  main,  and  10  ounces  in  the  hot  main,  and  that  all  bends 
in  the  mains  shall  be  less  than  45  degrees,  and  hence  negligible, 
except  one  in  each,  which  shall  be  90  degrees  and  equivalent  in 
resistance  to  25  feet  additional  pipe  of  about  2  feet  diameter,  then 
we  have,  according  to  the  formula, 


25,000  p 

Where,         d  -  diameter  of  pipe  in  inches, 
I  —  length  of  pipe  in  feet, 

v  =  number  feet  traveled  by  each  gas  particle  per  second. 
p  =  loss  of  pressure  in  ounces  per  square  inch, 
for  the  cold  blast  main,  if  the  velocity  is  100  feet  per  second. 

175  X  (100)2      1,750,000 

d  =  -  ----  —  ---       -  —  23.3  inches, 
25,000  X  3  75,000 

or,  virtually  2  feet,  and  for  the  hot  blast  main,  if  the  velocity  is  233 
feet  per  second, 

125  X  (233)2     0,786.100 
d  —  -----  —  =  27.1  inches. 

25,000  X  10        250,000 

or,  practically,  2XT4  feet. 

Air  Receivers  —  Unless  an  air  receiver  equal  in  volume  to 
at  least  four  piston  displacements  is  used  to  absorb  the  shock  of 
the  piston  impulses,  a  cold  blast  main  of  three  or  four  feet  in 
diameter  may  be  necessary  to  prevent  the  pipe  whipping.  A  re- 
ceiver is  preferable,  and  the  former  prejudice  against  it  is  disap- 
pearing because  liability  to  explosions  is  entirely  nullified  by. 
proper  arrangement  of  check-valves  in  the  hot  blast  main. 

BLOWING    ENGINES. 

In  order  to  determine  the  blowing  engine  capacity  required 
for  the  furnace,  it  is  necessary  to  know  the  quantity  of  air  and 
the  blast  pressure.  The  former  is  tolerably  fixed  for  a  given  size 
of  furnace,  but  the  latter  varies  with  furnace  conditions.  The 
average  theoretical  number  of  horse  power  needed  under  given 
conditions  is  represented  approximately  by  the  equation 

cubic  feet  per  m.  X  P.  per  square  foot. 


Horse-power  = 


33,000 


268 


Blast  Furnace. 


if  we  assume  that  the  pressure  in  the  air  cylinder  is  about  equal 
to  the  minimum  pressure  at  the  tuyeres. 

The  following  table,  based  on  this  formula,  represents  the 
approximate  number  of  horsepower  needed  for  various  quantities 
of  air  at  different  minimum  pressures : 


<r 
Pressure  per  square  inch.  .: 

20,000 
700 
785 
875 
900 
1,050 
1  135 

30,000 
1,050 
1,1SO 
1,330 
1,440 
1,570 
1,700 
1,830 
1,1)00 
2,005 
2,225 
2^355 

81 

40,000        50,000        00,000 
1,400          1,745      '    2,005 
1,570          1,900          2,335 
1,745          2,180          2,020 
1,920          2,400          2,880 
2,095          2,620          3,140 
2,270          2,835          3,405 
2,445          3,055          3,605 
2,620          3,270          3,930 
2,795          3,490          4,190 
2,905          3,710          4,450 
3,140          3,930          4,710 

108             135             162 

70,000 
2,445 
2,750 
3,055 
3,360 
3,605 
3,970 
4,275 
4,580 
4,890 
5,195 
5,500 

189 

12  pounds  

14  pounds  

1,220 
1,310 
1,400 
1,4S5 
1,570 

54 

15  pounds  

16  pounds  

]  7  pounds  

18  pounds  

Required    number     revolu- 
tions cylinder,  84  x  00  in. 

Expected   output   per   day, 

gross  tons : 

2,000  Ib.  fuel  per  ton...  260  390  515  645  775  900 
2,240  Ib.  fuel  per  ton.  ..  230  345  460  575  690  800 
2,500  Ib.  fuel  per  ton.  ..  210  310  415  515  620  725 

With  a  blowing  cylinder  84  inches  in  diameter  and  60  inches 
stroke  and  an  allowance  of  4  per  cent,  for  clearance,  each  revolu- 
tion of  the  engine  will  represent  370  cubic  feet  of  piston  displace- 
ment, and  hence  each  10,000  cubic  feet  will  require  about  27  revo- 
lutions of  the  engine. 

In  order  to  supply  35,000  cubic  feet  of  air  per  minute  from  a 
cylinder  84  X  60  inches  requiring  27  revolutions  for  each  10,000 
cubic  feet  of  air,  a  total  number  of  95  revolutions  will  be  neces- 
sary. As-  50  revolutions  is  about  the  limit  of  practicable  air- 
valve  speed,  and  hence  for  satisfactory  rilling  of  the  air  cylin- 
der, it  follows  that  two  air  cylinders  at  47^/2  revolutions  each 
will  be  necessary.  This  result  may  be  attained  by  one  cross-com- 
pound engine,  with  two  air  cylinders,  or  by  two  disconnected 
engines,  a  high  and  low  pressure  which  may  be  run  compound, 
with  one  air  cylinder  each.  This  allows  for  no  spares,  however,  so 
an  extra  engine  should  be  installed.  At  present,  vertical  cross- 
compound  engines  of  the  "  steeple "  type,  having  two  air 
cylinders,  are  extensively  used.  They  require  the  least  floor  space, 


Hints  on  Design  and  Equipment.  269 

but  owing  to  their  height  are  difficult  to  repair.  Moreover,  the 
stopping  of  one  engine  puts  two  air  cylinders  out  of  use.  There 
is  at  present  a  tendency  to  revert  to  the  old  long  cross-head  type 
of  single  engines,  as  being  simpler  and  less  wasteful  when  idle.  A 
high  and  low  pressure  pair,  with  a  spare  high  pressure  duplicate  is 
a  convenient  arrangement  for  single  furnaces.  For  a  pair  of  fur- 
naces one  spare  is  sufficient.  However,  single  engines  with 
tandem  air  and  steam  cylinders  are  never  smooth  running,  since 
there  is  no  compensation  for  the  throw  of  the  cranks  at  each  revo- 
lution. Smooth  running  may  be  promoted  by  the  use  of  the 
quarter-crank  principle,  by  which  twro  cranks  operating  on  the 
same  shaft  are  set  90  degrees  apart.  This  method  may  be  applied 
to  all  types  of  engine,  except  the  long  cross-head.  Horizontal  or 
vertical-horizontal  engines  obviate  excessive  heights  and  conse- 
quent vibration,  but  they  require  considerable  floor  space. 

Engines  are  now  usually  designed  to  run  compound  on  125  to 
150  pounds  initial  steam  pressure.  They  are  governed  to  show 
reasonable  economy  at  all  blast  pressures  between  12  and  20 
pounds  per  square  inch,  but  to  show  maximum  efficiency  at  15  to  16 
pounds.  The  usual  minimum  requirement  for  an  air  cylinder  for 
blowing  a  coke  furnace  is  20,000  cubic  feet  air  per  minute,  which 
is  equivalent  to  about  53  revolutions  with  an  air  cylinder  84  inches 
in  diameter  and  6o-inch  stroke.  With  most  air  valve  gearing  53 
revolutions  is  above  the  limit  of  speed  for  effective  action.  In 
consequence  air  cylinders  less  than  84  inches  in  diameter  have 
become  practically  obsolete,  and  some  makers  advocate  96-inch 
cylinders  with  slower  action. 

As  steam  pressures  at  a  furnace  plant  are  dependent  largely 
upon  the  condition  of  the  furnace  action,  and  consequently  upon 
the  supply  of  gas,  it  naturally  follows  that  they  frequently  fall 
below  125  pounds.  Many  engines  are  therefore  designed  to  run 
on  steam  pressure  as  low  as  100  pounds.  In  order  that -the  mean 
effective  pressure  in  the  low  pressure  steam  cylinder,  run  with 
a  good  vacuum,  may  always  overcome  the  resistance  offered  by 
the  back  pressure  of  the  blast,  even  when  the  steam  pressure  is  as 
low  as  100  pounds,  the  ratio  of  the  two  steam  cylinders  should  be 
small,  as,  for  example:  i  :  3.6  or  i  :  3.3.  For  a  low  pressure 
cylinder,  84  inches  diameter,  this  corresponds  to  high  pressure 


270 


Blast  Furnace. 


cylinders  of  44  or  46  inches  diameter.  With  steam  at  150  pounds, 
a  ratio  of  i  14  is  perfectly  efficient  and  permits  the  use  of  a  42-inch 
cylinder,  but  the  engine  may  fail  on  low  steam  pressures.  It  is 
better,  therefore,  to  use  large  high  pressure  cylinders  in  order  to 
be  prepared  for  low  steam  pressure  and  to  control  the  efficiency 


The  Southwark  Air  Cylinder,  Showing  Inlet  and  Outlet  Valves,  with  Gear. 

of  the  engine  when  running  on  high  steam  pressures  by  varying 
the  high  pressure  cut-off  in  such  a  way  as  to  give  the  low  pressure 
cylinder  steam  at  a  constant  pressure,  regardless  of  the  initial 
steam  pressure.  In  a  low  pressure  cylinder  of  the  same  area  as 
the  air  cylinder,  the  initial  pressure  should  not  fall  much  below 
50  pounds. 


Hints  on  Design  and  Equipment  271 

The  chief  distinguishing  characteristics  of  the  different  makes 
of  blowing  engines  lie  in  the  air  end,  and  are  centered  in  the 
design  and  action  of  the  air  valves.  In  order  that  air  cylinders 
may  furnish  blast  on  both  strokes  of  the  piston  they  must  be  fitted 
with  an  inlet  and  an  outlet  valve  at  each  end.  These  are  usually 
constructed  in  the  cylinder  heads  and  approximately  half  the  head 
is  devoted  to  each  valve. 

The  air  valves  of  the  Southwark  engines  are  of  the  rectangular 
gridiron  type  and  are  opened  and  closed  by  a  small  lateral  travel 
of  the  valves.  The  inlet  valve  is  operated  positively  throughout 
by  means  of  a  straight  cam  shaft.  It  starts  to  open  on  the  dead 
centre,  and  is  fully  open  at  10  per  cent,  of  the  stroke.  It  begins" 
to  close  at  90  per  cent,  of  the  stroke,  and  is  therefore  open  wide 
and  the  valve  is  stationary  for  80  per  cent,  of  the  stroke.  As  both 
opening  and  closing  are  absolutely  positive,  the  action  is  equally 
effective  at  all  speeds. 

The  outlet  valve  is  closed  positively  by  means  of  a  straight 
cam,  but  is  opened  automatically  by  the  action  of  the  blast  pres- 
sure. This  is  accomplished  by  means  of  a  by-pass  pipe,  leading 
from  the  interior  of  the  air  cylinder  to  a  small  auxiliary  cylinder, 
whose  piston  is  fitted  to  an  extension  of  the  valve  stem.  The 
outlet  valve  is  slightly  smaller  than  the  inlet. 

These  valves  are  guaranteed  to  operate  efficiently  at  80  revolu- 
tions per  minute,  and  are,  therefore,  well  adapted  for  use  in  gas 
blowing  engines  which  work  best  at  high  speeds.  They  are  used 
in  connection  with  the  Koerting  engines  which  operate  the  fur- 
naces of  the  Lackawanna  Steel  Company  at  Buffalo. 

The  air  cylinder  of  the  Mesta  Machine  Company's  blowing 
engine  has  a  positive  acting  rotary  inlet  valve  of  the  Corliss  type, 
extending  across  the  cylinder  head,  and  operated  by  means  of  a 
wrist-plate.  The  outlet  valves  are  circular  poppets,  usually  three 
in  number.  They  are  closed  mechanically,  but  opened  automati- 
cally by  the  blast  pressure  when  the  pressure  in  the  cylinder  equals 
that  in  the  blast  main.  The  valve  stem  carries  a  small  piston, 
working  in  a  dash-pot,  which  cushions  the  opening  movement. 
The  closing  is  accomplished  through  the  operation  of  the  wrist- 
plate.  When  the  stroke  is  nearly  complete,  a  sleeve  containing  a 
spiral  spring  engages  a  collar  on  the  valve  stem  and  forces  the 


272 


Blast  Furnace. 


'  i":  1149! 


valve  to  us  seat  just  as  the  piston  reaches  the  end  of  the  stroke. 
The  area  of  the  inlet  openings  is  about  12  per  cent.,  and  that  of 
the  outlet  about  10  per  cent,  of  the  piston  area.  The  maximum 
speed  of  operation  claimed  is  60  revolutions  per  minute. 

The  valves  used  on  the  air  cylinders  of  the  Tod  engines  are 
circular,  there  being  usually  two  inlet  and  three  outlet  valves  in 
each  cylinder  head.  The  inlet  valves  consist  of  double  ported 
pistons  working  in  cages  set  in  the  cylinder  heads.  The  valve  is 
operated  positively  by  means  of  levers  attached  to  a  wrist-plate 


The  Mesta  Air  Cylinder. 

which  opens  it  when  the  pressure  falls  to  that  of  the  atmosphere 
and  closes  it  at  the  dead  centre.  By  means  of  an  adjustable  link 
the  time  of  opening  is  varied  to  correspond  with  the  pressure  of 
the  blast. 

The  outlet  valve  is  of  the  poppet  type  which  opens  automati- 
cally  when  the  pressure  in  the  cylinder  equals  that  in  the  blast 
mains.  It  is  closed  positively  by  means  of  a  lever  operated  by  the 
wrist-plate.  The  area  of  the  valves  may  equal  12  per  cent,  of  the 
piston  area  and  they  can  be  operated  at  50  revolutions. 

The  Kennedy-Reynolds  vales  are  used  on  the  Allis-Chalmers 
•engines.  The  Kennedy  valve  is  the  inlet,  and  consists  of  a  hollow 


Tod  Air  Cylinder,  Showing  Operation  of  Valves. 


Head  of  Air  Cylinder  and  Parts  of  Inlet  and  Outlet  Valves  of  Tod  Blowing  Engine. 

273 


274 


Blast  Furnace. 


cast  iron  tube  passing  through  the  centre  of  the  cylinder.     It  is 
somewhat  objectionable,  as  it  allows  leakage,  owing  to  the  friction 
j^    of  rubbing,  and  also  necessitates  the  use  of  two  piston  rods.    The 
P.  loss.    outjet  or  Reynolds  valve  is  cup-shaped,  free  to  open  automatically, 
but  is  closed  positively.     Their  area  is  fully  equal  to  8  per  cent, 
of  the  piston  area,  and  they  can  be  operated  safely  at  30  revolu- 
tions per  minute. 


The   Kennedy-Reynolds  Valve. 

The  Weimer  blowing  cylinder  is  provided  at  each  end  with  a 
peripheral  extension  ring,  having  an  A-shaped  cross-section.  The 
ring  is  pierced  on  each  slope  by  a  series  of  slots  y±  inch  wide, 
closed  by  aluminum  strips.  The  slots  on  the  outer  slope  act  as 
inlet  valves  and  those  on  the  inner  slope  as  outlet  valves.  Each 
set  of  valves  equals  19  per  cent,  of  the  cylinder  area,  and  they 
are  all  operated  automatically  by  the  pressure  of  the  air. 


Hints  on  Design  and  Equipment. 


275 


POWER  REQUIREMENT. 

Blowing.  — In  the  case  of  a  furnace,  for  example,  which 
requires  35,000  cubic  feet  of  air  per  minute  at  a  minimum  pres- 
sure of  15  pounds  per  square  inch  at  the  furnace,  we  see  by  the 
table  that  the  air  requirement  will  demand  about  2300  H.  P.  theo- 
retically at  the  furnace,  or  about  2500  at  the  engine.  One  theoreti- 
cal H.  P.  per  minute  requires  42.42  B.  T.  U.,  hence  a  total  of 
42.42  X  2500  =  106,000  B.  T.  U.  per  minute,  or  6,360,000  B,  T. 
U.  per  hour  will  be  required  to  furnish  the  blast. 


The   Weimer  Valve. 

Owing  to  lack  of  economical  efficiency  in  engines  and  boilers, 
the  actual  requirement  of  power  is  much  greater.  It  may  be  esti- 
mated approximately  as  follows : 

Assuming  a  compound  condensing  engine,  when  running  on 
steam  at  150  pounds  pressure,  to  consume  about  16  pounds  of 
steam  per  indicated  H.  P.,  utilizing  18.75  B.  T.  U.  per  pound  of 
steam  per  minute.  16  X  18.75  =3°°  B.  T.  U.  per  I.  H.  P.  per 
minute  or  18,000  B.  T.  U.  per  hour.  As  42.42  X  60  =  2545 
B.  T.  U  per  hour  is  a  theoretical  H.  P.,  this  indicates  a  thermal 
efficiency  of 

2545  X  ioo 


18,000 


14.14  per  cent. 


276  Blast  Furnace. 

Reckoning  a  mechanical  efficiency  on  both  ends  of  the  engine  of 
87  per  cent,  of  the  indicated  thermal  efficiency  gives  an  actual 
thermal  efficiency  of  12.3  per  cent.  Assuming  a  boiler  efficiency 
of  65  per  cent,  the  fuel  efficiency  of  the  system  would  be  12.3  X 
.65  =  8  per  cent.  The  quantity  of  heat  required,  therefore,  to 
blow  the  furnace  per  hour  will  be 

6,360,000X100  TT 

•~ g —  79,5oo,ooo  B.  T.  U. 

79,500,000 

—  =  69,300  pounds  of  gas. 
1147 

Hoisting. — The  power  expended  in  hoisting  the  stock  may 
be  found  as  follows.  Under  the  present  assumption  the  quantity 
of  stock  raised  per  ton  of  pig  is, 

Coke 1.0  tons. 

Ore 1.7  tons. 

Stone 0.5  tons. 

Total 3.2  tons. 

The  quantity  of  stock  required  each  hour  by  a  400  ton  furnace  will 
be  3.2  X  2240  X~  -  —  119,400  pounds.  Assuming  for  an  80 

foot  furnace  that  the  total  vertical  height  from  the  stockhouse 
floor  to  the  dumping  point  is  no  feet,  then,  neglecting  the  weight 
of  the  skips  since  they  should  be  balanced,  the  total  work  required 
will  be,  119,400  X  no  =  13,134,000  foot  pounds  per  hour. 

13,134,000    =  i6^g8o  B    T    ^     Assuming  the  efficiency  of  the 

77« 
hoisting  engine  to  be  10  per  cent  of  that  of  the  blowing  engine, 

16,880  X  ioo 

this  would  require  an  expenditure  of  -   0 =  2,110,000 

O.o 

B.  T.  U.,  which  is  equivalent  to  -  =  1840  pounds  of  gas 

per  hour. 

Pumping. — Assuming  that  10,000  gallons  of  cooling  water 
are  required  per  ton  of  iron  produced,  then  4,000,000  gallons  are 
needed  by  the  furnace  in  24  hours,  and  the  power  required  to 
pump  this  quantity  may  be  determined  as  follows: 

4,000,000   X   8^ 

—  —  1,400,000  pounds  of  water  per  hour. 

A  25  pound  pressure  at  the  tuyeres  requires  a  head  of  65  feet 


Hints  on  Design  and  Equipment  277 

above  the  working  level  of  the  furnace.  Assuming  the  source 
of  the  water  supply  to  be  35  feet  below  this  level,  there  will  be 
a  total  lift  of  100  feet.  The  total  work  done  by  the  pumps  per 
hour  will  then  be  1,400,000  X  100  =  140,000,000  foot  pounds 

140,000,000  ,          TT 

-  =  180,000  B.  T.  U. 

•       778 

Assuming  a  pump  efficiency  of  20  per  cent,  which  is  .23  of  that  of 
the  blowing  engine,  we  will  have  a  thermal  requirement  of 

180,000  X  loo  ,      T,   ™   TT       ,  .  , 

—  =  9,782,600  B.  T.  U.,  which  equals, 


0.23  X  8 

9,782,600  .       , 

^2L —  8530  pounds  of  gas  per  hour. 

Feed    Water. — If  the  blowing  engine  uses  16  pounds  of  steam 
per  H.  P.  per  hour,  the  quantity  of  -feed  water  required  will  be 

1 6  X  25oo  =  40,000  pounds  per  hour, 

but  steam  required  for  other  uses  will  bring  this  amount  up  to 
50,000  pounds  at  least.  The  total  head  against  the  pumps  will  be 
something  in  excess  of  the  boiler  pressure  of  150  pounds.  Let 
us  assume  160  pounds  for  example.  Then  the  total  work  done 
by  the  pumps  will  be, 

50,000  X  1 60  =  8,000,000  foot  pounds  per  hour. 
8,000,000 


—  10,280  B.  T.  U. 
is  10  per  cent.,  this 
=  1,285,000  B.  T.  U. 


778 

If  the  efficiency  of  the  pumps  is  10  per  cent.,  this  work  will  require 
10,280  X  100 


0.8 

which  equals     '"'    =  1120  pounds  of  gas  per  hour. 

1147 

Lighting.  — The  power  necessary  to  light  a  plant  by  means 
of  electricity  and  to  run  an  ore  bridge,  larry  and  machine  shop 
may  be  estimated  if  the  number  and  character  of  lights  and  the 
power  of  the  motors  is  known.  Assuming  that  25  arc  and  100 
incandescent  lights  are  used,  then 

25  X  700  =  1 7,500  watts. 
100  X     50=     5, 000  watts. 

Total  power  =  22,500  watts. 

2,545 
One  watt  hour  —  —   —  =  3.4  B.  T.  U. 

746 
3.4  X  22,500  =  7G,50A  B.  T.  U. 


278  Blast  Furnace. 

Assuming  the  same  efficiency  as  the  blowing  engine,  gives 

70.300  X  100 

-  -  956,250  B.  T.  U.  per  hour. 
8 
950,250 

—  =  835  pounds  gas  per  hour. 
1,147 

Power — Assuming  5-50  H.  P.  motors  for  the  other  uses,  we 
have, 

250  X  2,545  =  636,250  B.  T.  U.,  which  at  the  same  efficiency  will  require 
636,250  X  100 

—  —  7,953,150  units,  or 
8 
7,953,150 

—  —  6,935  pounds  of  gas. 
1,147 

Summary. — The  total  power    developed  and   gas  consumed 
may  be  summarized  thus : 

Pounds  gas 

H.  P.  per  hour. 

Blowing 2,500  69,300 

Hoisting 70  1,840 

Cooling   water 310  8,530 

Feed    water 40  1,120 

Lighting    30  835 

Power    250  6,935 


Totals 3,200  88,560 

which  is  about  8  H.  P.  per  ton  of  coke  burned.    Gas  required  per 

88,s6o 

H.  P.  =  -r-2. —  —  27.7  pounds. 
3200 

Gas  Distribution — The  percentage  of  the  total  gas  gen- 
erated with  a  fuel  consumption  of  2240  pounds  coke  per  ton  of 
pig  which  is  consumed  in  power  development,  is 

88.560  X  100  Per  cent. 

— =    41.5 

213,250 
Percentage  of  gas  utilized  in  heating  blast  — 27.0 

Total  usefully  applied  =   68.5 

Leaving  for  other  purposes  and  losses  — 31.5 

The  following  summary  is  designed  to  show  the  thermal  effi- 
ciency of  the  blast  furnace  under  various  fuel  consumptions : 

Fuel  consumption 2.000  lb.  2,240  Ib.  2,500  lb. 

Carbon  burned  to  CO  per  100 

pounds   pig 39  lb.  46.9  lb.  56  lb. 

Carbon  burned  to  CO2  per  100 

pounds  pig 29  lb.  29.0  lb.  29  lb. 

Total   carbon    burned   per 

100  pounds  pig 68  lb.  75.9  lb.  85  lb.     - 


Hints  on  Design  and  Equipment 


279 


630,655  B.  T.  U.       671,150  B.  T.  U. 


Total  heat  developed  per  100 

pounds    pig 595,500  B.  T.  U. 

Total    heat   possible    per    100 

pounds    pig 989,400  B.  T.  U.   1,104,345  B.  T.  U.   1,236,750  B.  T.  U. 

Under  ordinary  conditions: 
Heat  utilized  in  the  furnace  .591,000  B.  T.  U. 
Heat  utilized  in  the  stoves.  .164,920  B.  T.  U. 


591,000  B.  T.  U. 
177. 300  B.  T.  U. 


591,00GB.  T.  U. 
189,000  B.  T.  U. 


Heat  utilized  in  the  boilers.  .250,230  B.  T.  U.       272,500  B.  T.  U.       294,840  B.  T.  U. 

Total  heat  "usefully  ap- 
plied  ".  1,006,150  B.  T.  U.  1,040,800  B.  T.  U.  1,074,840  B.  T.  U. 

Percentage  of  possible  heat..      100.2  94.2  86.9 

Under  ideal  conditions: 

Heat  utilized  in  the  furnace. 591, 000  B.  T.  U.  591,000  B.  T.  U.  591,000  B.  T.  U. 

Heat  required  for  the  blast.  .  108,150  B.  T.  U.  120,720  B.  T.  U.  135,200  B.  T.  U. 

Heat   required  for  powoi- 73,300  B.  T.  U.  81,440  B.  T.  U.  91,210  B.  T..  U. 

Total    heat    required 772,450  B.  T.  U.       793,160  B.  T.  U.       817,410  B.  T.  U. 

Percentage  of  possible  heat.  .        78.1  71.8  66.1 

BOILERS. 

The  boiler  capacity  necessary  to  run  all  the  forms  of  power 
development  of  a  400  ton  furnace  is,  as  we  have  seen,  3200  H.  P. 
The  type  of  boiler  best  suited  to  gaseous  fuel  is  the  water  tube, 
and  its  use  has  become  practically  universal  for  blast  furnace 
work.  The  make  most  generally  used  is  probably  the  Babcock 
and  Wilcox,  although  the  Stirling  is  becoming  very  popular  also. 
They  are  both  of  the  horizontal  drum  variety.  The  Stirling, 
however,  has  curved  tubes  which  do  not  lend  themselves  readily 
to  cleaning.  The  Cahall  and  Wheeler  makes  are  watertube  vertical 
boilers,  and  are  also  considerably  used.  The  Cahall  is  expensive 
to  maintain  and  is  not  growing  in  favor.  The  Wheeler  is  cheaper 
to  install,  gives  less  trouble,  and  stands  more  abuse. 

The  boiler  plant  should  always  have  at  least  one  spare  unit 
for  use  during  cleaning  and  repairs.  The  size  of  unit  should 
range  from  200  to  400  H.  P.,  according  to  the  size  of  plant.  The 
unit  should  not  be  so  large  in  proportion  that  one  more  or  less 
seriously  affects  the  steam  capacity.  Experience  shows  that  never 
less  than  6  to  8  PL  P.  is  needed  per  ton  of  iron.  When  pressure 
is  above  12  pounds,  and  electric  machinery  has  to  be  operated  in 
the  yard,  8  to  10  H.  P.  are  needed..  Ordinarily  i  square  inch  of 
gas  burner  area  is  sufficient  to  maintain  I  boiler  H.  P. 

PUMPS. 

The  piston  pump  has  long  been  used  to  furnish  cooling  water 
to  the  blast  furnace  plant,  but  of  late  there  is  a  growing  applica- 


280  Blast  Furnace. 

tion  of  the  centrifugal  pump.  Of  whatever  form  is  used,  there 
should  not  be  less  than  three  units,  of  which  two  are  of  the 
requisite  capacity  and  the  third  is  a  spare.  To  furnish  4,000,000 
gallons  daily,  three  two  million  gallon  pumps  should  be  provided. 
A  14  x  10  plunger  operated  at  54  revolutions  will  furnish 
2,000,000  gallons  in  24  hours. 

For  boiler  feed,  the  positive  acting  piston  pump  is  required. 
The  plunger  pump  with  outside  packing  is  most  desirable.  Two 
units  are  sufficient  under  ordinary  conditions.  Two  plungers, 
6  x  10  inches  at  35  strokes  per  minute,  will  furnish  feed  water 
for  a  400  ton  furnace. 

GAS    ENGINES. 

Owing  to  the  admittedly  low  thermal  efficiency  of  steam  equip- 
ment in  general,  and  to  the  fact  that  blast  furnace  gas  is  well 
adapted  to  direct  combustion  in  gas  engines,  there  has  been  con- 
siderable application  of  gas  engines  to  blast  blowing  work. 

It  is  found  as  a  rule  that  about  11,500  B.  T.  U.  suffices  to 
develop  a  brake  horse  power  when  its  energy  is  expended  in  the 
cylinder  of  a  gas  engine.  This  indicates  a  thermal  efficiency  of 

2S4S  X  100 

JHO          —  =  22  per  cent. 
11,500 

11,500                                                        ,  .  ,  .      10.9  X  ioo 
— —  -=  10.9  pounds  of  gas  per  H. P., which  is    -    -  

—  39  per  cent,  of  that  required  by  the  steam  engine  per  H.  P. 

34,880  X  ioo 
10.9  X  3200  —  34,880  pounds  gas  per  hour,  or 

—  J6-35  per  cent,  of  the  gas  generated. 

41.5  per  cent.  --  16.35  Per  cent-  =  25-I5  Per  cent>  or  over  /4 
of  the  total  gas  may  thereby  be  saved  for  other  uses.  25.15  per 
cent.  +31.5  per  cent,  makes  a  total  of  56.65  per  cent,  of  gas 
which  might  be  utilized  for  other  purposes.  The  quantity  of  gas 
so  wasted  equals, 

213,250  X  -5665  =  120,800   pounds. 

If  10.9  "pounds  gas,  exploded  in  a  gas  engine,  is  capable  of  produc- 
ing I  H.  P.,  then  the  power  so  saved  will  equal, 

=  1 1, 080  H.  P.,  or  about  28  H.  P.  per  hour 

10.9 


Hints  on  Design  and  Equipment 


281 


B  B 
.^  ^ 


i«- 


y.  £  Q  O 

fD     fD     PS     P 


nj  2>oo 

o   2   c   c 


5535=- 
»  5  j5  J5  5 


K-  ?•  --S  ?  a  s.  a  ?i  °  r<!  *3" 


a  a  s  «  *  1  § 

S  §  M  B  '•"  |  « 

»<•-<<                C  3  3 

as,*  •  S  i  a 

^     ^     ~  GJ  fD 

53  ?  "•'  S  S-  ^ 

m  £   c-  cr  tr.  _  «> 


- 
'      " 


§  B  era  w 

p  ^" 

'JS  2  w  P 

w  ^  B 


jr 
goo' 

b    O 

•a  73   M  co 

fD     fD     Cil    00 


t-  *-  g 

0  0  3 


re   rt-    c    C 


M    *J|   0 

W  ^0 


o  o 

** 


'« 


S|l§ 

list 


*>.  a  c 

00     i'l 

2;  o  ^3  ' 

~  a  05'  • 


c«        o 
W        W 


§ 


d'iJb 

o    o 


§     W 
>    w 


5    poo  S 

it !  o  o  o 

I  >3  -a  M  co^j 

11  g.sl 

o  o  b  b  o 


M    tO 

0    Oi 
tO   tx5 


PP 

*-*    *-k 

r*  r* 


I-*  *•  O  I    CO  »*>•  tO 

ci  w  1 1  b  I  bi  w  b 

"^  <t  1-1      >-s  n  n 

fD  fD  fD         fD  fD  fD 


M   CO 

•a  xs 

fD    fD 


CO   CO   tO 

OJ   O   VI 

111 

o    o    o 

fD     fD     f» 
000 


M   P" 
O 


O   fi 

b  5» 


a^    I 
w      a 

fe.  ? 


cr 

•       CJ1 
O 

o 


d5 


282 


Blast  Furnace. 


per  ton  of  pig  made.  However,  the  saving  which  can  be  credited 
purely  to  the  use  of  gas  engines  for  necessary  po\ver  develop- 
ment will  be  only 

X  28  =  12.5  H.  P  per  ton  of  product, 


since  the  remainder  was  already  in  excess  of  the  requirement. 

The  Koerting  Gas  Engine,  built  by  the  De  La  Yergne  Machine 
Company,  is  a  two-cycle,  double-acting  engine,  taking  impulses 
on  both  strokes  in  the  same  manner  as  a  steam  engine.  Gas  and 
air  are  forced  by  separate  pumps  into  each  end  of  the  cylinder 
alternately.  They  mingle  as  they  enter  and  are  ignited  by  electric 
sparks.  The  exhaust  openings  are  in  the  periphery  of  the 
cylinder  at  the  middle,  so  that,  owing  to  the  length  of  the  piston, 
they  are  not  uncovered  until  toward  the  end  of  the  stroke,  thereby 
obviating  the  necessity  for  exhaust  valve  mechanism. 

In  the  diagram  the  power  piston  is  represented  as  just  starting 
toward  the  rear  end  of  the  cylinder  and  the  pump  pistons  are  just 
starting  toward  the  crank  end.  Explosion  has  just  taken  place. 
Gas  and  air  are  being  forced  into  the  connecting  passages'  under 
compression.  The  admission  valve,  however,  is  held  closed  by 
the  high  pressure  in  the  cylinder  and  further  ingress  is  impossible 


Diagram  Showing  Arrangement  of  Gas  and  Air  Ducts  of  Koerting  Double  Acting 

Gas  Engine. 


Hints  on  Design  and  Equipment 

until  the  exhaust  ports  are  uncovered.  The  fresh  air  and  gas 
then  rush  in,  and  sweep  out  the  products  of  the  previous  explosion. 
They  are  compressed  again  by  the  returning  piston,  preparatory 
to  being  ignited  in  turn. 

The  two-cycle  engine  shows  an  average  mechanical  efficiency 
of  only  75  to  80  per  cent,  owing  to  the  expenditure  of  power  in 
operating  the  gas  and  air  pumps.  The  slightly  higher  efficiency 
of  four-cycle  engines  is  offset,  however,  by  the  liability  to 
derangement  of  their  highly  complex  valve  mechanism.  On  the 
other  hand  the  total  number  of  cylinders  involved  in  the  four-cycle 
engine  is  less,  and  there  is  at  present  a  tendency  to  adopt  it  for 
blast  furnace  work. 

With  blast  furnace  gas  giving  a  mean  effective  pressure  of 
about  65  pounds  per  square  inch,  1000  Brake  H.  P.  will  be 
delivered  by  a  double-acting  cylinder  38  x  60  inches  operated  at 
75  revolutions.  Such  a  cylinder  could  drive  a  72  inch  air  cylinder 
delivering  20,000  cubic  feet  of  air  against  15  pounds  pressure,  or 
a  60  inch  cylinder  delivering  14,000  cubic  feet  at  25  pounds 
pressure. 

In  the  face  of  emergencies,  however,  gas  engines  lack  the 
flexibility  of  steam  engines.  They  have  little  or  no  overload 
capacity.  Excessive  demands  on  a  steam  engine  may  be  met  by 
higher  steam  pressures  or  later  cut-off.  With  the  gas  engines 
the  quantity  of  gas  and  pressure  of  explosion  is  tolerably  constant. 
It  is  necessary,  therefore,  to  design  a  gas  engine  for  the  maximum 
duty  required  of  it,  and  operate  it  as  near  full  load  as  possible. 
Hence,  an  84-inch  air  cylinder  at  15  pounds  pressure  can  be  op- 
erated by  a  42-inch  gas  cylinder,  whereas  a  pressure  of  25  pounds 
demands  a  cylinder  54  inches  in  diameter,  which  must  be  provided 
if  such-  a  contingency  is  to  be  met  by  a  single  engine.  Since  the 
maximum  economy  of  the  gas  engine  is  realized  only  when  it  is 
operated  at  full  load,  it  is  better  to  design  engines  for  ordinary 
loads  and  to  meet  emergencies  by  utilizing  reserve  units. 

GAS    WASHING. 

Since  gas  engines  require  a  gas  which-  is  practically  free  from 
solid  matter  an  efficient  system  of  gas  washing  is  necessary.  The 
quantity  of  dust  remaining  in  the  gases  should  not  exceed  o.i 
grains  per  cubic  foot. 


284 


Blast  Furnace. 


Gas  Cleaning  Plant  at  the  Lackawanna  Steel  Company. 


Hints  on  Design  and  Equipment  285 

The  gas-washing  apparatus  used  at  the  Lackawanna  plant  in 
Buffalo  consists  essentially  of  a  dust  catcher  (A),  followed  by 
cooling  towers  (D),  which  contains  Koerting  water-spray  nozzles, 
and  by  hydraulic  fans  (F)  in  which  the  gas  is  beaten  violently  £!15*-230' i906- 
with  water.  The  gas  is  then  led  away  through  pipes  (G.  H.)  to 
engines  and  stoves  (B).  The  cleaned  gas  is  said  to  contain  only 
0.02  grains  solid  matter  per  cubic  foot  of  gases. 

The  Bian  apparatus  used  in  Germany  reduces  the  dust  to  o.oi 
grains  per  cubic  foot  of  gases.  It  consists  essentially  of  perforated 
discs,  rotating  10-12  times  per  minute  in  a  tank  half  filled  with 
water,  through  whose  moistened  perforations  the  gas   is  forced 
by  means  of  a  fan,  followed  by  filtering  towers  to  remove  the   l53.«f&ee, 
moisture.     The  cost  of  installation  is  about  $60  per  1000  cubic   r 
feet  of  gas  cleaned,  the  water  consumption  is    12  gallons,  the 
H.  P.  required  0.3,  and  the  cost  of  operating  7^  cents. 

The  Theisen  washer,  which  is  in  high  favor  abroad,  consists 
of  a  cylinder  supplied  with  water,  into  which  the  gas  is  forced 
while  the  cylinder  is  rotated  850  times  per  minute.  The  purifica- 
tion is  very  complete  at  moderate  cost.  Per  1000  cubic  feet  of 
gas  the  costs  are  said  to  be  as  follows :  Installation,  $23 ;  water 
consumption,  9  gallons;  power  consumed,  0.15  H.  P.;  operating 
expenses,  3.8  cents. 

ROLLING   STOCK. 

All  rolling  stock  equipment  should  be  standard  gauge,  and 
fitted  with  standard  and  interchangeable  parts,  such  as  trucks, 
couplers,  etc. 

Hot  metal  and  cinder  cars  should  have  heavy  framework, 
firmly  bolted  together,  connecting  the  trucks.  Structural  weakness 
may  have  disastrous  results. 

Iron  Ladles. — Hot  metal  requires  5  cubic  feet  space  per 
ton,  and  a  2O-ton  car,  therefore,  must  have  100  cubic  feet  net 
capacity.  A  car  having  5  feet  average  diameter  and  5  feet  avail- 
able depth  will  hold  20  tons.  About  20  per  cent,  extra  depth 
should  be  allowed,  however,  for  skulling  and  to  prevent  slopping 
on  curves  and  grades.  The  lining  must  be  of  refractory  bricks 
and  not  less  than  4]^  inches  thick.  For  tapping  a  4oo-ton  furnace 
every  six  hours,  five  such  ladles  will  be  required,  not  counting 
spares. 


286  Blast  Furnace. 

Cinder  Ladles The  molten  cinder  requires  about  15  cubic 

feet  per  ton  and  a  1 5-ton  cinder  car  requires  225  cubic  feet  net 
capacity.  A  bowl  having  7  feet  average  diameter  and  6  feet  avail- 
able depth  will  contain  230  cubic  feet.  The  cinder  bowl  may  be 
lined  with  firebricks,  or  with  a  cast  iron  thimble  which  is  remov- 
able. The  latter,  however,  is  of  no  avail  when  molten  iron  is 
tapped  with  the  cinder,  as  it  cuts  through  the  thimble  and  the 
cinder  flows  over  the  tracks.  In  dumping,  the  ladles  should 
always  travel  forward,  in  order  to  clear  the  track.  If  the  furnace 
makes  half  a  ton  of  cinder  for  each  ton  of  iron,  or  50  tons  in  six 
hours,  it  will  evidently  require  the  pretty  constant  services  of  at 
least  four  cinder  cars. 


SUPPLEMENT. 

USES    OF    PIG    IRON. 

GRADES    OF    PIG    IRON. 

In  the  manufacture  of  ferrous  products  pig  iron  exhibits  a 
wide  range  of  usefulness.  It  is  not  only  used  practically  un- 
changed to  produce  castings  of  a  great  variety  of  form  and  quality, 
but  it  is  the  starting  point  of  all  present  methods  of  producing 
wrought  iron  and  steel.  Since  each  subsequent  operation  de- 
mands a  composition  which  is  within  certain  limits,  it  follows  that 
pig  iron  must  necessarily  offer  a  considerable  variety  of  com- 
position. The  usually  specified  limits  of  the  chief  grades  of  pig 
iron  are  as  follows : 


Grade  of  iron. 
No.  1  foundry 

Si.  per  cent. 
2  50  to  3  00 

S,  per  cent, 
under  0  035 

P,  per  cent.  Mn 
0  5  to  1  0 

,  per  cent. 

No.  2  foundry 

•>  00  to  °  50 

0  5  to  1  0 

No.  3  foundry.  .  .  . 

1.50  to  2.  00 

under  0.055 

0.5  to  1  0 

under  1.0 

Malleable    

0  75  to  1  50 

under  0  050 

Gray    forge  

......    .    under  1  50 

under  0  100 

Bessemer    

1  00  to  2  00 

under  0  050 

Low   phosphorus  . 

under  2  00 

under  0  030 

under  00*? 

Basic    

under  1  00 

under  0  050 

Thcinas    Cilchrist 
Bessemer    . 

or    basic 
.    under  1.00 

under  0.050 

2.0  to  3.0 

1.0  tn  2.ft 

CLASSIFICATION    OF    PIG    IRONS. 

According  to  their  uses,  pig  irons  may  be  separated  roughly 
into  two  great  classes,  first,  those  which  undergo  complete  conver- 
sion into  other  forms  of  ferrous  products,  and,  second,  those 
which  are  not  materially  changed  in  composition  or  nature. 

In  the  first  class  are  included  all  grades  which  are  intended 
primarily  for  use  in  the  manufacture  of  wrought  iron  and  steel, 
such  as  gray  forge,  Bessemer,  basic,  low  phosphorus  and  Thomas 
irons.  In  the  second  class  are  the  foundry  and  malleable  grades, 
although,  as  we  shall  see  later,  the  malleable  grade  properly 
stands  between  the  foundry  and  conversion  irons  in  this  classifica- 
tion. 

CONVERSION    OF    PIG    IRON. 

The  object  of  conversion  is  identical  in  all  cases.  It  consists 
essentially  of  the  elimination  of  as  much  as  possible  of  all  the 

287 


288  Blast  Furnace. 

non-ferrous  elements  which  arc  present  in  the  pig.  Differences 
in  the  resulting  products  naturally  follow  from  differences  in  the 
converting  processes  employed.  The  most  obvious  distinction 
between  the  various  converting  processes  is  based  upon  the  state 
of  the  product.  When  the  resulting  metal  is  in  a  completely  fused 
state  it  receives  the  name  of  steel,  when  in  a  pasty  or  semi-fused 
state  it  is  known  as  wrought  iron.  This  difference  of  condition 
in  conversion  gives  to  these  two  types  of  product  physical  charac- 
teristics which  differ  far  more  than  the  chemical  compositions, 
and  is  therefore  the  basis  of  distinction  between  them  in  this 
country. 

WROUGHT     IRON     CONVERSION. 

The  process  of  conversion  which  has  wrought  iron  for  its 
product  is  known  as  puddling.  The  grade  of  pig  which  is  designed 
primarily  for  this  process  is  gray  forge.  The  operation  is  carried 
on  in  a  reverberatory  furnace,  which  consists  essentially  of  a  low 
rectangular  chamber  built  of  firebrick  and  having  a  low  dividing 
wall,  cutting  off  about  one-third  of  its  length.  The  larger  por- 
tion is  the  working  chamber  and  the  smaller  is  the  fireplace.  The 
fuel  used  is  long  flame  bituminous  coal.  The  flame  passes  over 
the  dividing  wall  or  bridge  and  heats  the  working  chamber  by 
radiation  on  its  way  to  the  chimney.  In  this  way  the  charge  is 
kept  from  contact  with  the  fuel  itself. 

Nature  of  Hearth. — The  composition  and  arrangement  of 
the  hearth  material  of  the  puddling  furnace  are  of  first  impor- 
tance to  the  process.  The  hearth  bottom  is  usually  made  up  of 
some  refractory  material,  over  which  a  layer  of  roll-scale  is  spread 
and  made  to  soften  and  cohere  by  firing.  Then  a  ball  of  wrought 
iron  scrap  is  worked  back  and  forth  over  the  hearth  at  welding 
temperature,  thereby  giving  it  a  smooth,  even  coat  of  magnetic 
oxide.  The  side  walls  are  then  fettled.  The  fettling  consists. of 
oxides  of  iron,  usually  in  the  form  of  dense,  lumpy  ore,  either 
hematite  or  magnetite.  It  is  arranged  around  the  walls  of  the 
furnace  at  the  slag  level  in  such  a  way  as  to  give  the  hearth  a 
dished  shape.  The  fettling  serves  a  double  purpose :  it  protects 
the  firebrick  walls  from  the  corrosion  of  the  slag,  and  it  furnishes 
oxygen  for  oxidizing  the  metalloids  of  the  charge.  This  is  prob- 


Uses  of  Pig  Iron.  289 

ably  accomplished  chiefly  through  the  medium  of  the  slag,  which 
acts  as  a  carrier  of  the  oxygen  in  the  form  probably  of  Fe3O4. 

Operation.  — The  charge  for  two  men  consists  of  about  l/2 
ton  of  pig  iron.  Its  introduction  into  the  furnace  is  preceded  by 
50  to  100  pounds  of  slag  from  a  previous  heat,  in  order  to  insure 
slag  early  in  the  operation.  The  melting  stage  occupies  about 
half  an  hour,  at  the  end  of  which  the  metal  is  in  a  state  of  quiet 
fusion.  During  this  stage  the  greater  part  of  the  silicon  and  man- 
ganese and  some  of  the  iron  have  been  oxidized  to  SiCX,  MnO, 
and  FeO  and  Fe.,Oa,  respectively,  and  have  united  with  each  other 
to  form  a  slag  which  is  a  silicate  of  iron  and  manganese.  By 
means  of  a  rabble,  the  whole  charge  is  then  stirred,  to  bring  the 
metal  into  contact  with  the  fettling,  the  newly  formed  slag  and 
the  air,  by  which  the  carbon  can  be  oxidized.  CO  is  formed  and 
given  off  as  bubbles,  which  give  the  bath  the  appearance  of  boil- 
ing. The  charge  foams  up  and  some  of  the  slag  overflows.  Then 
the  reaction  becomes  less  violent  and  gradually  subsides  as  the 
carbon  is  eliminated  and  the  iron  is  said  to  "  come  to  nature." 
This  iron  is  no  longer  fusible,  but  exists  as  globules  of  metallic 
iron  whose  melting  point  is  above  the  temperature  of  the  furnace. 
It  is  necessary  then  to  collect  these  detached  masses  into  balls. 
The  time  of  heat  is  y2  to  2  hours.  The  balls  are  withdrawn 
from  the  furnace  dripping  with  slag,  which  fills  all  of  the  inter- 
stitial spaces,  and  are  sent  to  a  hammer  or  "  squeezer."  Here  the 
bulk  of  the  slag  is  squeezed  out  and  the  ball  compacted  into  a  kind 
of  billet  which  goes  at  once  to  the  rolls  and  is  rolled  into  a  flat 
bar,  about  ^l/2  x  -xs  inch  in  section,  which  is  known  as  "muck- 
bar."  The  muck  bar  is  subsequently  sheared,  piled  and  rerolled 
into  finished  iron. 

Elimination  of  Metalloids — In  the  order  of  elimination,  sili- 
con stands  first.  The  elimination  is  accomplished  through  the 
oxidation  of  Si  to  SiO2,  in  which  condition  it  can  no  longer  unite 
with  the  metal,  but  must  transfer  itself  to  the  slag.  This  opera- 
tion is  generally  complete  by  the  time  fusion  is  accomplished.  The 
oxidation  of  silicon  is  more  rapid  and  complete  at  low  tempera- 
tures, because  at  high  temperatures  oxygen  shows  a  preference  for 
carbon.  At  low  temperatures  carbon  will  not  be  attacked  as  long 
as  silicon  is  present. 


290  Blast  Furnace. 

It  is  apparent  that  the  presence  of  much  silicon  in  forge  irons 
has  several  disadvantages.  In  the  first  place,  as  just  stated,  it 
defers  the  elimination  of  carbon  and  prolongs  the  operation  by 
just  that  amount.  In  the  second  place,  it  makes  more  slag.  The 
quantity  of  slag  is  determined  by  the  quantity  of  silicon  present. 
The  slag  is  mainly  ferroso-ferric  silicate,  having  about  30  per  cent. 
SiCX,  and  50  per  cent,  metallic  iron.  The  ratio  of  Si  to  Fe  is  there- 
for about  i  14.  Consequently,  every  pound  of  Si  in  the  slag  means 
also  the  presence  of  4  pounds  of  Fe.  This  large  apparent  loss  is 
partly  compensated,  however,  by  the  fact  that  the  oxidation  of  Si 
by  Fe3O4  of  the  slag  according  to  the  reaction, 

Fe304  +  2Si  ===  3Fe  +  2SiO2, 

yields  3  pounds  Fe  for  every  pound  Si  oxidized.  A  third  disad- 
vantage of  much  Si  in  the  pig  is  due  to  the  fact  that  highly  sili- 
ceous slags  are  less  able  to  carry  P  and  S.than  basic  slags.  To  be 
sure,  a  certain  quantity  of  slag  is  essential  to  the  well-working 
of  the  process,  but  it  is  very  evident  that  any  excess  is  not  simply 
a  loss  of  so  much  metal  to  the  purchaser,  but  is  positively  detri- 
mental. 

The  elimination  of  manganese  follows  that  of  silicon  so  closely 
that  it  is  almost  simultaneous  with  it.  Like  silicon,  it  is  prac- 
tically all  eliminated  and  must  therefore  be  reckoned  as  a  dead 
loss  in  purchasing.  Its  elimination  is  accomplished  by  oxidation 
also.  While  all  of  the  Mn  is  oxidized,  its  oxidation  is  only  par- 
tial since  most  of  it  enters  the  slag  as  MnO,  instead  of  MnCX. 
MnO  acts  as  a  base  and  unites  with  SiO2.  It  does  not  tend  to 
increase  the  quantity  of  slag  as  SiCX  does,  but  simply  helps  to 
satisfy  the  SiCX,  thereby  liberating  an  equivalent  weight  of  iron 
from  the  slag.  When  the  manganese  is  oxidized  by  the  oxides  in 
the  slag,  according  to  the  reaction, 

Fe304  +  4Mn  =±  3Fe  +  4MnO, 

each  pound  of  Mn  yields  ^4  pound  of  Fe.  The  gross  saving  for 
each  pound  of  Mn,  therefore,  may  amount  to  1^4  pounds  Fe. 

The  elimination  of  phosphorus  is  not  so  rapid  as  that  of  silicon 
and  manganese,  nevertheless  about  half  is  removed  during  the 
melting  period.  It  must  be  eliminated  fairly  early  in  the  opera- 
tion, while  the  temperature  is  low.  The  removal  of  phosphorus 


Uses  of  Pig  Iron.  291 

is  also  effected  through  oxidation,  by  which  it  enters  the  slag, 
but  at  high  temperatures  oxygen  shows  a  preference  for  carbon, 
and  it  will  desert  the  phosphorus  which  has  been  oxidized,  leaving 
it  in  the  elemental  condition,  so  that,  perforce,  it  must  return  to 
the  metal.  Its  elimination  is  facilitated  by  removing  before  the 
temperature  rises  too  high  the  slag  first  formed,  which  contains 
the  greater  part  of  silicon  and  phosphorus.  The  slag  subsequently 
formed  will  necessarily  be  more  basic  on  account  of  the  absence 
of  silica,  and  will  therefore  hold  the  oxides  of  phosphorus  more 
tenaciously.  Even  under  the  most  favorable  conditions,  the  re- 
moval of  phosphorus  is  never  as  complete  as  that  of  silicon  or 
manganese.  Probably  never  more  than  90  per  cent.,  and  gener- 
ally not  over  75  per  cent.,  of  the  phosphorus  is  removed  in  pud- 
dling. It  is  probable,  however,  that  much  of  the  remainder  exists 
in  the  slag  in  the  oxidized  condition  and  so  does  not  exert  its 
usual  deleterious  effects  on  the  metal.  The  oxidation  of  phos- 
phorus by  the  slag,  according  to  the  reaction, 

5Fe304  +  4?2  ==  iSFe  +  4P2O5, 

shows  a  yield  of  over  3  pounds  of  iron  for  every  pound  of  phos- 
phorus oxidized. 

The  elimination  of  sulphur  is  the  last  and  the  least  satisfactory 
of  all,  for  which  reason  it  is  highly  desirable  that  it  should  be  kept 
low  in  the  blast  furnace,  which  is  the  best  place  for  its  elimination. 
In  the  puddle  furnace  the  average  elimination  is  probably  not  over 
half  of  the  quantity  present.  Sulphur  may  be  eliminated  either  in 
the  elemental  or  oxidized  condition — either  by  volatilization  or  by 
scorification.  The  elimination  is  very  slight  at  first,  but  increases 
rapidly  toward  the  end.  This  is  probably  due  to  the  fact  that 
sulphur  is  decidedly  volatile  and  cannot  resist  the  higher  tem- 
peratures of  the  later  stages.  It  is  also  carried  away  by  a  basic 
slag  which  we  have  seen  to  be  favored  toward  the  end  of  the 
operation.  The  presence  of  manganese  favors  the  removal  of  sul- 
phur, owing  to  the  stability  of  manganese  sulphide. 

Influence  of  Slag. — We  have  seen  that  an  excessive  amount 
of  slag  is  likely  to  be  a  cause  of  serious  waste  in  puddling.  When 
properly  proportioned,  however,  it  is  capable  of  yielding  a  com- 
pensatory return  of  metal  through  the  reduction  by  the  metalloids 
of  the  oxides  of  iron  derived  from  the  fettling.  For  this  reason 


292  Blast  Furnace. 

it  is  usual  for  the  process  to  make  on  the  average  a  yield  of  pud- 
dled bar  nearly  equal  to  the  weight  of  pig  used.  The  proper 
amount  of  slag  is  the  least  quantity  that  will  carry  the  burden  of 
metalloids  and  properly  protect  the  iron  from  oxidation.  An 
attempt  to  puddle  too  dry  with  a  deficiency  of  cinder  will  leave 
the  iron  exposed  to  the  oxidizing  flame.  As  a  result,  much 
will  be  lost  through  the  stack  as  fumes  of  iron  oxide.  On  the 
other  hand,  the  oxidation  of  the  remaining  metal  will  not  be  prop- 
erly neutralized  by  the  scanty  supply  of  slag,  and  even  if  it  can 
be  properly  balled  up,  the  resulting  bar  will  probably  show  lack  of 
cohesion,  being  red  shcrt  or  cold  short  or  both. 

Character  of  Product — Bars  of  wrought  iron  which  have 
been  produced  by  rolling  puddled  balls  show  certain  character- 
istics which  distinguish  them  from  their  counterpart,  mild  steel. 
A  freshly  sheared  or  fractured  surface  will  show  small  black  spots, 
which  are  never  present  in  steel.  These  spots  are  the  exposed 
ends  of  filaments  of  slag  which  have  been  drawn  out  by  rolling 
from  the  globules  imprisoned  in  the  squeezed  ball.  The  fineness 
of  the  markings  serves  as  a  rough  guide  to  the  amount  of  rolling 
to  which  the  piece  has  been  subjected.  Again,  if  a  bar  be  nicked 
and  bent  cold,  the  fracture  at  the  bend  will  show  a  silky  lamina- 
tion or  fibrous  structure,  while  the  steel  fracture  is  always  crys- 
talline. The  fibrous  structure  also  is  attributed  to  the  drawing  out 
of  globules  of  metal,  interspersed  with  particles  of  slag.  The 
quantity  of  slag  so  imprisoned  is  never  as  great  by  wreight  as  it 
appears,  since  the  slag  is  of  much  lower  specific  gravity  than  the 
iron.  The  quantity  may  range  from  0.2  per  cent,  to  over  2  per 
cent,  by  weight,  depending  upon  the  care  taken  in  making  and 
refining  the  iron.  A  considerable  proportion  of  the  phosphorus 
and  sulphur  which  analysis  shows  to  be  in  wrought  iron  is  present 
in  the  oxidized  condition  in  this  slag.  It  is,  therefore,  not  injuri- 
ous, as  when  combined  with  the  metal.  It  was  formerly  argued 
that  the  superior  welding  qualities  of  wrought  iron  are  due  to  the 
presence  of  this  slag,  which  acts  as  a  flux  for  any  scale  or  oxide 
films  that  may  cover  the  surfaces  during  heating  and  interfere 
with  perfect  metallic  contact.  Experiment  shows,  however,  that 
high  slag  irons  do  not  weld  any  better  than  those  containing  little 
slag.  It  is  difficult  to  see  how  such  action  could  well  be  expected 
of  a  silicate  which  is  already  saturated  with  oxides  of  iron. 


Uses  of  Pig  Iron.  293 

Composition  of  Product — The  analysis  of  wrought  iron  may, 
as  a  rule,  be  expected  to  fall  within  the  following  limits : 

C.  Si.  Mn.  P.  S.  Fe. 

0.05-0.25  0.02-0.2  Tr.-O.l  0.05-0.2  0.02-0.1  99.8-99.0 

From  the  preceding  discussion,  therefore,  it  is  evident  that 
the  initial  amount  of  P  should  not  exceed  I  per  cent. ;  that  S 
should  not  rise  much  above  o.i  per  cent.;  that  silicon  should  be 
limited  to  what  is  needed  to  create  sufficient  cinder,  and  that 
manganese  might  as  well  be  absent. 

STEEL     CONVERSION. 

There  are  four  chief  grades  of  iron  which  have  conversion 
into  steel  as  their  ultimate  design — namely,  Bessemer,  low  phos- 
phorus, basic  and  Thomas-Gilchrist  grades.  They  are  each  de- 
signed for  a  certain  method  of  conversion  and  are  not  adapted, 
generally,  to  use  in  any  of  the  other  methods.  The  Bessemer 
grade  is  naturally  designed  for  the  Bessemer  process,  and  includes 
by  far  the  largest  tonnage  of  all  the  conversion  grades.  The  basic 
grade  of  iron  is  second  in  this  country  in  quantity  used  and  is 
rapidly  overtaking  Bessemer.  It  is  designed  especially  for  basic 
open  hearth  conversion.  The  low-phosphorus  grade  is  naturally 
expensive,  and  therefore  has  not  a  very  wide  application.  It  is 
intended  especially  for  conversion  in  acid  open  hearth  furnaces, 
particularly  for  making  highest  grade  steel  castings  and  special 
steels.  The  Thomas-Gilchrist  grade  is  intended  only  for  the 
basic  Bessemer  process,  which  has  now  no  application  whatever 
in  this  country. 

Classification  of  Steel  Conversion  Methods — Of  the  four 
processes  of  conversion  that  have  steel  for  their  immediate  object, 
viz. :  Bessemer,  Thomas-Gilchrist,  acid  open  hearth  and  basic  open 
hearth,  the  natural  classification,  based  on  method  of  operating, 
would  be  to  distinguish  the  Bessemer  and  Thomas  methods  from 
the  open  hearth  methods.  The  two  former  consist  essentially 
of  purifying  pig  iron  in  a  nearly  closed  vessel  by  means  of  a  blast 
of  air.  .  For  this  reason,  they  are  sometimes  known  as  the  "pneu- 
matic" processes.  The  two  latter  consist  essentially  of  melting 
the  iron  on  a  dish-shaped  hearth  and  purifying  it  by  means  of  iron 
ore  thrown  into  the  metallic  bath. 

But  from  the  standpoint  of  the  composition  of  the  pig  iron 


294  Blast  Furnace. 

to  be  used,  it  is  more  important  to  distinguish  them  according  to 
what  they  can  accomplish  in  the  way  of  purification  of  the  metal. 
For  this  reason,  we  shall  consider  them  under  the  heads  of  acid 
and  basic  methods. 

Acid  Processes — As  we  have  seen  already,  the  composition 
of  the  slag  is  a  most  potent  factor  in  the  purification  of  metals. 
It  is  obvious,  also,  that  it  is  impossible  to  control  the  composition 
of  a  slag  if  the  furnace  lining  itself  is  practically  a  limitless  reser- 
voir of  undesirable  ingredients.  It  is  necessary,  therefore,  in 
order  to  produce  certain  results  in  purification,  that  the  nature 
of  the  lining  in  the  converting  furnace  should  have  careful  consid- 
eration. 

We  have  seen  repeatedly  that  silicon  and  manganese  are  nat- 
ural slag-makers,  and  that  when  in  the  oxidized  state  they  enter 
slags  indiscriminately  and  regardless  of  slag  composition.  For 
the  removal  of  such  elements  the  composition  of  the  slag  need  not 
be  controlled  within  narrow  limits  and  the  least  expensive  type  of 
furnace  lining  may  be  selected.  Siliceous  rocks  or  sands  are  the 
cheapest  refractory  materials  obtainable  and  may  be  used  as  lin- 
ings under  the  above  conditions.  Since  silica  is  an  acid  radical,  a 
siliceous  lining  will  naturally  permit  a  slag  of  acid  predominance, 
and  the  process  is  therefore  known  as  an  "  acid  "  process.  The 
Bessemer  and  acid  open  hearth  methods  fall  under  this  head. 

Basic  Processes — When  it  is  desirable  or  necessary  to  elimi- 
nate phosphorus  and  sulphur,  as  well  as  silicon  and  manganese,  we 
know  that  a  basic  slag  is  necessary ;  and  therefore  in  order  to  limit 
rigidly  the  supply  of  acid  ingredients  in  the  slag,  the  lining  must 
be  of  basic  material:  The  most  successful  basic  refractory  ma- 
terials so  far  discovered  are  specially  prepared  magnesite  and 
dolomite,  which,  on  account  of  expense,  are  never  used  unless 
demanded  by  the  composition  of  the  iron  to  be  converted.  Under 
this  head  fall  naturally  the  basic  open  hearth  and  the  Thomas- 
Gilchrist,  or,  as  it  is  generally  called,  the  basic-Bessemer  process. 

BESSEMER     PROCESS. 

The  Bessemer  process,  which  was  invented  by  Bessemer  in 
1856,  but  not  introduced  here  until  1867,  consists  essentially  of 
pouring  molten  iron  into  a  pear-shaped  vessel,  called  a  "  con- 


Uses  of  Pig  Iron.  295 

verter,"  and  blowing  through  it  a  blast  of  atmospheric  air  until 
it  removes  such  impurities  as  the  nature  of  the  process  permits, 
namely,  silicon,  manganese  and  carbon. 

The  converting  vessel  is  a  steel-riveted  shell,  some  20  feet 
high  by  10  to  12  feet  in  diameter,  reinforced  and  set  on  trunnions 
to  facilitate  rotation,  having  one  end  contracted  to  small  diameter 
and  the  other  closed  by  a  detachable  bottom.  An  air  pipe  leads 
from  one  trunnion  which  is  hollow  to  an  air  box  which  is  attached 
to  the  bottom,  and  which  communicates  with  the  tuyeres  set  in 
the  bottom.  The  lining  is  at  least  a  foot  thick  and  may  be  made 
up  of  various  materials,  such  as  blocks  of  millstone  grit  or  ground 
quartz  mixed  with  fireclay,  or  silica  bricks,  etc.,  all  of  which  are 
refractories  of  highly  siliceous  character.  The  lining  is  therefore 
denominated  "  acid." 

Operation.  — The  method  of  operating  a  Bessemer  converter 
is  as  follows :  The  vessel  is  turned  down  into  the  horizontal  posi- 
tion and  a  charge  of  molten  pig  iron,  usually  15  to  20  tons,  from 
a  blast  furnace  or  cupola  is  poured  in  at  the  nose  of  the  vessel. 
A  blast  of  air,  having  a  pressure  of  about  25  pounds  per  square 
inch,  is  turned  into  the  vessel  through  the  bottom  tuyeres  and  the 
vessel  is  turned  up  into  the  vertical  position.  We  then  have  the 
spectacle  of  some  20  tons  of  molten  iron  kept  in  violent  ebullition 
by  a  constant  current  of  air,  whose  force  is  sufficient  to  keep  the 
fluid  metal  from  running  into  the  tuyere  openings  beneath  it. 

Elimination  of  Metalloids. — The  immediate  result  of  the 
action  of  the  air  upon  the  molten  metal  is  the  oxidation  of  the 
silicon  and  manganese.  The  resulting  SiO2  and  MnO,  together 
with  some  oxides  of  iron,  immediately  unite  to  form  a  slag.  This 
period  is  characterized  by  a  scanty  flame  coming  from  the  nose 
of  the  vessel,  since  very  little  volatile  gas  is  formed  before  the 
carbon  is  attacked.  The  oxidation  of  silicon  liberates  a  large  quan- 
tity of  heat  and  quickly  brings  the  temperature  up  to  the  point  of 
carbon  ignition.  If  the  temperature  is  allowed  to  rise  too  quickly, 
carbon  will  exert  its  preferential  power  over  the  oxygen,  and  the 
silicon  and  manganese  will  not  be  completely  eliminated.  The 
high  temperature  can  be  controlled  by  charging  cold  scrap  into  the 
converter  during  the  blow,  or  by  introducing  steam  with  the  blast. 

The  disadvantage  of  too  much  silicon  and  manganese  is  more 


296  Blast  Furnace. 

apparent  here  than  in  puddling,  because  the  action  is  not  so  de- 
pendent upon  the  presence  of  slag  or  upon  its  composition.  As 
before,  they  both  represent  so  much  waste  to  the  purchaser,  and 
do  not  compensate  by  reducing  an  equivalent  of  iron.  The  man- 
ganese, however,  renders  the  slag  more  fluid,  and  at  the  same  time 
displaces  its  equivalent  of  iron,  thereby  protecting  the  iron  from 
excessive  scorification.  The  silicon,  on  the  other  hand,  does  not, 
as  in  puddling,  determine  the  quantity  of  slag  absolutely,  as  the 
walls  of  the  vessel  naturally  add  to  the  quantity  of  silica,  and  con- 
sequently help  in  the  carrying  off  of  iron.  The  quantity  of  silicon 
affects,  however,  the  length  of  blow,  since  the  oxidation  of  carbon 
must  not  begin  until  the  silicon  is  practically  eliminated.  It  was 
formerly  thought  necessary  to  have  2  to  3  per  cent,  silicon  in  order 
to  raise  the  temperature  of  the  metal  sufficiently,  but  with  more 
rapid  running  it  is  found  that  I  per  cent,  is  ample. 

Generally  at  the  end  of  three  or  four  minutes,  the  carbon  begins 
to  burn.  The  oxidation  of  carbon  produces  CO  in  the  converter. 
As  the  CO  reaches  the  outer  air,  it  bursts  into  flame,  forming  CO2. 
This  period  is  marked  by  a  long,  brilliant  flame  at  the  nose  of  the 
vessel,  and  represents  the  maximum  temperature  attained.  It  has 
been  calculated  by  J.  W.  Richards  that  the  rise  in  temperature 
from  that  of  the  molten  pig  iron  during  a  blow  is  nearly  600  de- 
grees V.,  which  brings  the  temperature  of  the  product  well  above 
the  melting  point  of  wrought  iron.  If  the  flame  shows  a  deficiency 
of  heat  at  this  period  the  temperature  can  be  increased  by  tilting 
the  vessel  until  some  of  the  tuyeres  are  no  longer  covered  by  the 
metal.  Unconsumed  air,  entering  through  these  tuyeres,  burns 
the  CO  within  the  converter  and  thereby  raises  the  temperature 
of  the  vessel.  Some  iron  is  also  oxidized,  which  increases  the 
additional  heat  developed. 

At  the  end  of  about  ten  minutes  the  carbon  has  been  eliminated 
and  the  flame  drops.  The  vessel  is  then  turned  down  and  a  glow- 
ing mass  of  wrought  iron,  practically  free  from  silicon  and  man- 
ganese, and  having  less  than  o.i  per  cent,  carbon,  is  ready  to  pour 
into  the  ladle.  A  recarburizer,  usually  molten  "  spiegeleisen,"  is 
added  to  the  metal  in  the  converter  before  it  is  emptied.  This 
recarburizer  contains  a  definite  percentage  of  carbon  and  manga- 
nese, which  brings  the  composition  of  the  resulting  steel  to  the 
desired  limits. 


Uses  of  Pig  Iron.  297 

A  modification  of  this  process,  carried  on  in  a  small  vessel 
with  side  tuyeres  and  a  low  blast  pressure  is  known  as  the  Tro- 
penas  process,  and  is  considerably  used  in  making  small  steel  cast- 
ings. 

Influence  of  Slag — A  study  of  the  composition  of  Bessemer 
slags  reveals  the  cause  of  the  limitations  of  the  process.  Bessemer 
slags  vary  widely  in  composition,  but  the  SiO2  rarely  falls  much 
below  50  per  cent.,  while  it  may  rise  to  nearly  70  per  cent.  The 
bulk  of  the  remainder  is  made  up  of  the  combined  oxides  of  iron 
and  manganese,  the  proportion  of  each  being  governed  by  the 
initial  quantity  of  manganese.  We  have  already  seen  that  a  blast 
furnace  slag  having  as  little  as  30  per  cent.  SiO2  is  not  sufficiently 
basic  to  carry  off  phosphorus,  and  even  when  the  SiO2  falls  to 
20  per  cent.,  as  in  the  puddling  process,  the  extraction  of  phos- 
phorus is  far  from  complete.  It  is  impossible,  therefore,  to  expect 
any  elimination  of  phosphorus  in  the  Bessemer  process.  As  a 
purifier  from  silicon,  manganese  and  carbon  it  is  unparalleled  for 
speed  and  economy,  but  as  an  extractor  of  phosphorus  or  sulphur 
it  has  no  claims  whatever. 

Composition  of  Bessemer  Pig — With  regard  to  the  limits 
of  silicon,  the  Bessemer  pig-iron  maker  is  between  two  fires.  The 
silicon  must  not  be  so  low  that  the  heats  will  run  cold,  and 
thereby  have  no  scrap-carrying  power,  or  demand  tilting,  which 
wastefully  oxidizes  iron,  nor  should  it  be  so  high  as  to  -create 
an  excessive  quantity  of  slag  or  unduly  prolong  the  time  of  blow. 
For  these  reasons,  silicon  should  not  fall  much  below  i  per  cent, 
on  the  average  or  rise  above  2  per  cent.,  and  manganese  is  only 
so  much  waste.  As  regards  phosphorus  and  sulphur,  since  the 
Bessemer  process  is  entirely  unable  to  eliminate-  any  portion  of 
them,  they  will  increase  in  percentage  through  concentration,  be- 
cause they  remain  unaffected  while  the  quantity  of  metal  is  dimin- 
ished by  8  to  10  per  cent,  during  conversion.  They  should  there- 
fore be  carefully  limited  in  the  pig  to  about  90  per  cent,  of  that 
allowable  in  the  steel. 

The  final  composition  of  Bessemer  steel  generally  falls  between 
these  limits : 

C.  Si.  Mn.  P.  S.  Fe. 

Percent.  Percent.          Percent.  Percent.  Percent.  Percent. 

0.05-l.fi  Tr.-0.05  0.3-1.0  Below  0.1  Below  0.08  99.5-98.0 


298  Blast  furnace. 

ACID     OPEN      HEARTH      PROCESS. 

The  open  hearth  process,  which  was  introduced  in  this  country 
shortly  after  the  Bessemer  process,  consists  essentially  of  melting 
a  mixture  of  pig  iron  and  scrap  on  a  dish-shaped  hearth  and 
oxidizing  and  removing  certain  impurities  by  means  of  iron  ore 
and  slags  of  suitable  composition. 

The  open  hearth  furnace  consists  of  a  large,  horizontal  rect- 
angular chamber,  built  of  very  refractory  bricks,  properly  bound 
by  buckstays.  The  working  chamber  is  usually  about  30  x  15  feet, 
and  holds  50  tons  of  molten  metal.  At  each  end  of  the  chamber 
are  ports,  which  serve  alternately  as  inlets  for  fuel  gas  and  air 
which  burn  in  the  chamber,  and  as  outlets  for  the  products  of 
combustion.  Each  gas  and  air  port  connects  with  an  underground 
chamber  filled  with  checker  brickwork  through  which  at  one  end 
the  gas  and  air  enter,  and  at  the  other  the  products  of  combustion 
escape.  The  heat  extracted  by  the  checkers  from  the  waste  gases 
serves,  on  reversing,  to  heat  the  entering  gas  and  air.  The  fur- 
nace is  known  as  the  Siemens  regenerative  furnace.  Its  system  of 
preheating  the  fuel  and  air  easily  permits  the  attainment  of  steel- 
melting  temperature. 

Character  of  Charge — The  bottom  of  the  acid  open  hearth 
furnace  is  composed  of  very  refractory  silica  sand  which  is  fused 
in  place.  This  fact  determines  the  character  of  the  slag  and  the 
limitations  of  the  method.  Upon  this  bottom  of  sand  the  metal 
is  charged,  melted  and  purified.  A  striking  difference  between  the 
pneumatic  and  regenerative  systems  of  conversion  lies  in  the 
character  of  the  charge.  In  the  Bessemer  process  we  saw  that 
it  consisted  entirely  of  molten  pig  iron.  In  the  open  hearth  proc- 
ess it  may  consist  either  of  molten  or  of  cold  pig.  Furthermore, 
the  open  hearth  charge  rarely  consists  wholly  of  pig  iron,  but  a 
considerable  quantity  of  steel  and  wrought  iron  scrap  is  charged 
also.  The  proportion  of  pig  iron  used  in  the  charge  of  an  acid 
furnace  should  be  such  that  when  the  charge  is  melted,  the  sili- 
con and  manganese  will  have  been  eliminated  and  the  bath  will 
contain  y2  to  I  per  cent,  of  carbon.  Under  ordinary  conditions 
this  requires  20  to  30  per  cent,  of  pig  and  the  remainder  scrap. 

Operation. — The  method  of  operating  an  open  hearth  fur- 
nace has  for  its  first  step  the  charging  of  material  into  the  fur- 


Uses  of  Pig  Iron.  299 

nace.  This  was  formerly  done  by  hand  by  means  of  a  long  iron 
"  peel,"  and  this  method  is  still  used  at  some  of  the  smaller 
plants.  It  is  slow,  keeping  the  furnace  open  a  long  time  and 
increasing  oxidation.  The  more  usual  method  is  to  fill  the  fur- 
nace by  means  of  specially  designed  boxes,  handled  by  a  Wellman 
charging  machine.  A  5O-ton  heat  may  be  charged  in  this  way  in 
less  than  an  hour.  Rapid  charging  permits  less  loss  of  metalloids 
and  admits  of  using  less  pig  iron  in  consequence.  The  rational 
system  of  charging  is  to  place  the  scrap  on  the  hearth  first  and  to 
place  the  pig  iron  on  top  of  the  scrap.  The  covering  of  pig  pre- 
vents the  scrap  from  oxidation  by  the  flame,  and  at  the  same  time 
it  melts  first  and  trickles  down  over  the  scrap,  thereby  carburizing 
and  dissolving  it.  Hard  firing  should  melt  a  heat  completely  in 
three  or  four  hours.  When  the  metal  is  all  under  the  slag  and 
shows  by  test  to  be  hot  and  still  high  in  carbon,  lumps  of  ore  are 
thrown  into  the  bath  at  intervals  to  oxidize  the  carbon.  Careful 
watch  of  the  carbon  content  tells  when  the  heat  has  reached  the 
desired  point,  whereupon,  if  the  metal  is  hot  enough,  it  is  tapped. 
Ferromanganese  and  sometimes  coke  dust  are  thrown  into  the 
ladle  to*recarburize  and  remanganize  the  metal  to  suitable  com- 
position. 

Elimination  of  Metalloids. — As  in  the  case  of  the  acid  Bes- 
semer process,  the  silicon  and  manganese  are  eliminated  first,  their 
elimination  being  generally  accomplished  by  the  time  the  fusion 
is  complete.  As  SiO2  and  MnO  they  unite  with  whatever  oxides 
of  iron  are  present  to  form  the  slag.  The  slag  floats  on  the  top 
of  the  metal  and  prevents,  to  a  great  extent,  any  further  oxidation 
by  the  flame.  The  elimination  of  the  carbon  is  accomplished  chiefly 
by  the  ore  which  is  thrown  into  the  bath.  The  evolution  of  CO 
agitates  the  bath,  mixing  it  and  facilitating  the  action.  Here 
again,  carbon  exercises  its  control  over  oxygen,  and  if  the  tem- 
perature is  too  high  it  will  take  it  even  from  the  slag.  Both  iron 
and  silicon  may  be  reduced  by  it.  The  former  action  is  a  desirable 
recovery  of  lost  iron,  but  the  latter  introduces  silicon  and  gives  a 
porous  metal. 

Composition  of  Pig — The  presence  of  silicon  in  pig  for  the 
acid  open  hearth  process  has  no  advantages.  Here,  unlike  the 
Bessemer  processes,  there  is  no  need  of  silicon  to  furnish  heat, 


300  Blast  Furnace. 

because  the  bath  is  amply  heated  by  fuel  gas.  Silicon  is  so  much 
loss  to  the  purchaser.  Although  a  certain  amount  of  slag  is  neces- 
sary as  a  covering  to  the  bath,  yet  silicon  is  not  absolutely  neces- 
sary to  its  formation,  as  the  sand  of  the  hearth  bottom  could  fur- 
nish enough  for  the  purpose.  Since  all  the  silicon  is  usually 
oxidized  by  the  flame,  it  does  not  compensate  in  any  way  by  re- 
ducing an  equivalent  of  iron  from  the  ore.  In  other  words,  it  is 
wholly  undesirable,  although  in  moderate  quantities  it  does  no 
harm  and  tends  to  protect  the  hearth  from  excessive  scorification 
during  the  slag-forming  period.  A  high  percentage  of  silicon 
would  prolong  the  operation  and  cause  large  loss  of  iron  by  form- 
ing an  excessive  quantity  of  slag.  It  would  compensate  partially 
for  this  loss,  however,  by  reducing  metal  from  the  ore,  since  there 
would  be  an  unoxidized  excess  of  silicon  after  melting,  which 
would  be  removed  by  the  ore  additions. 

The  presence  of  manganese  also  presents  no  advantages  in  this 
process.  It  is  oxidized  and  enters  the  slag,  displacing  an  equiva- 
lent of  iron,  to  be  sure,  but  that  does  not  affect  the  percentage 
yield,  since  it  was  purchased  as  so  much  iron.  It  tends  to  make 
the  slag  more  fusible. 

The  oxidation  of  the  residual  carbon  by  means  of  the  ore,  re- 
sults in  the  formation  of  CO  and  metallic  iron,  in  accordance  with 
the  reaction, 

3FexC  +  Fe203  =  3CO  +  Fex  +„ 

thereby  yielding  an  equivalent  of  iron  to  the  bath  of  3.1  pounds 
Fe  for  each  pound  of  C.  The  CO  thus  formed,  bubbles  up  through 
the  slag  and  burns  at  the  surface,  yielding  additional  heat. 

The  elimination  of  phosphorus  and  sulphur  in  the  acid  open 
hearth  process  is  subject  to  the  same  limitations  as  in  the  Bessemer 
process.  Acid  open  hearth  slags  usually  have  a  silica  content  of 
about  50  per  cent.,  which  is  far  too  acid  to  permit  the  retention  of 
appreciable  quantities  of  either  element.  Indeed,  such  a  slag  may 
permit  the  transmission  of  noticeable  quantities  of  sulphur  from 
the  gases  to  the  metal,  and  thereby  give  rise  to  an  increase  of 
sulphur  in  the  bath.  All  of  the  phosphorus  and  much  of  the 
sulphur  present  in  the  ore  incorporate  themselves  in  the  metal. 
It  is  evident,  therefore,  that  these  elements  should  be  strictly  lim- 
ited, not  only  in  the  pig  iron,  but  also  in  the  scrap,  ore  and  fuel. 


Uses  of  Pig  Iron.  301 

Low  Phosphorus  Pig. — The  limits  which  are  imposed  on  the 
^composition  of  pig  which  is  to  be  converted  by  this  process  vary 
with  the  class  of  products  desired.  The  limits  of  Si  and  Mn  are 
naturally  not  so  stringent  as  those  of  P  and  S,  and  as  they  both 
are  completely  eliminated,  a  given  content  of  each  is  equally  suit- 
able for  all  purposes.  With  the  P  and  S,  however,  the  case  is 
different.  When  it  is  desired  to  make  metal  of  exceptional  quality, 
such  as  government  steel  castings,  ordnance,  etc.,  which  has  speci- 
fications calling  for  P  and  S  below  0.035  Per  cent.,  it  is  necessary 
to  produce  a  pig  having  these  elements  not  far  above  0.030  per 
cent.  Furthermore,  it  'must  be  used  only  in  connection  with 
selected  scrap  and  ore.  This  grade  of  pig  has  consequently  re- 
ceived the  name  "  low  phosphorus  "  pig,  although  it  must  be 
equally  low  in  sulphur.  On  the  other  hand,  for  structural  steels, 
plate,  etc.,  whose  specifications  are  not  too  low,  Bessemer  pig,  or 
a  mixture  of  Bessemer  pig  with  low  phosphorus  pig  or  with  low 
phosphorus  scrap,  will  bring  the  desired  composition.  It  must  be 
remembered  that  not  only  does  all  of  the  P  and  much  of  the  S 
present  in  the  bath  congregate  in  the  metal,  but  there  is  likely 
to  be  an  apparent  increase  of  them  through  concentration  as  the 
other  metalloids  are  eliminated. 

The  final  composition  of  acid  open  hearth  steels  generally  falls 
between  the  following  limits : 

C.  Si.  Mn.  P.  S.  Fe. 

Percent.  Percent.         Percent.  Percent.  Percent.  Percent. 

0.05-1.5  Tr.-0.3  0.3-0.7  0.03-0.10  0.03-0.08  99.5-98.0 

BASIC     OPEN     HEARTH     PROCESS. 

This  modification  of  the  open  hearth  process  was  not  intro- 
duced into  this  country  until  1888.  The  furnace  used  in  the 
process  is  identical  with  that  used  in  its  acid  counterpart,  except 
in  regard  to  the  lining  below  the  slag  line.  As  the  name  implies, 
the  slag  of  this  method  is  of  basic  predominance,  and  in  order  to 
maintain  its  basic  character  must  be  kept  from  contact  with  sili- 
ceous materials  as  much  as  possible.  It  is  customary,  therefore, 
to  make  the  furnace  bottom  of  basic  material.  The  best  construc- 
tion consists  of  a  thin  lining  of  magnesite  bricks,  covered  with  a 
heavy  layer  of  calcined  magnesite,  which  is  sintered  with  a  small 


302  Blast  Furnace. 

percentage  of  some  fusible  material  such  as  a  basic  slag.     Dolo- 
mite is  sometimes  used  as  a  substitute  for  magnesite. 

Character  of  Charge — The  charge  of  the  basic  furnace,  like 
that  of  the  acid,  is  made  up  of  pig  iron  and  scrap,  except  that  the 
proportion  is  somewhat  different.  Owing  to  more  oxidation  dur- 
ing melting,  a  larger  percentage  of  pig  must  be  used.  The  pig 
usually  ranges  from  35  to  60  per  cent,  of  the  charge,  and  may  be 
either  molten  or  solid.  Besides  the  metallic  materials,  a  non- 
metallic  portion,  known  as  the  "basic  addition,"  is  used.  This 
consists  usually  of  limestone  or  burnt  lime,  and  iron  ore.  Its 
object  is  to  neutralize  the  silica  formed  by  the  silicon  oxidized  dur- 
ing the  melting  period,  and  to  prevent  it  from  attacking  the  hearth. 
For  this  reason,  the  additions  are  charged  first  and  spread  over 
the  furnace  bottom,  and  upon  them  the  metallic  charge  is  placed. 
The  quantity  of  basic  material  should  be  sufficient  to  neutralize 
completely  the  silica  present  and  must  therefore  be  varied  ac- 
cording to  the  content  of  silicon  in  the  pig  used.  The  resulting 
slag  should  have  about  three  times  as  much  CaO  -j-  MgO  as  SiCX. 
Elimination  of  Metalloids — The  oxidation  in  this  process 
follows  the  usual  order.  During  melting,  silicon,  manganese  and 
phosphorus  are  oxidized  in  the  order  named.  The  resulting  oxides 
trickle  down  with  the  molten  iron  and  come  in  contact  with  the 
basic  additions  on  the  furnace  bottom.  The  limestone  has  mean- 
while been  partially  calcined  and  the  lime  unites  to  form  the  slag. 
The  SiO2  and  the  P2O5  are  taken  up  readily  by  the  oxides  of 
calcium  and  iron,  but,  owing  to  the  presence  of  such  an  excess  of 
bases,  the-MnO  is  not  absorbed  so  readily,  and  therefore  its  elimi- 
nation from  the  metal  is  not  so  rapid  and  complete  as  in  the  acid 
processes.  The  SiO2,  on  the  other  hand,  is  snapped  up  eagerly 
and  held  so  firmly  by  the  very  basic  slag  that  it  is  not  materially 
affected  by  the  preference  of  oxygen  for  carbon,  even  at  the  high- 
est temperatures.  Approximately  60  per  cent,  of  the  phosphorus 
and  65  per  cent,  of  the  carbon  on  an  average  are  oxidized  during 
melting.  The  elimination  of  the  phosphorus  follows  closely  that 
of  carbon,  and  with  a  properly  basic  slag  the  removal  of  phos- 
phorus is  practically  complete  by  the  time  the  heat  is  done.  Under 
ordinary  conditions  a  proper  slag  can  usually  be  relied  upon  also 
to  extract  at  least  50  per  cent,  of  the  sulphur  originally  present. 


Uses  of  Pig  Iron.  303 

Influence  of  Slag — The  basic  process  was  devised  to  enable 
the  steel  maker  to  cope  with  phosphorus  and  sulphur.  As  they 
both  form  acid  radicals,  it  is  only  by  means  of  extreme  basicity 
that  they  can  be  securely  held  in  the  slag  in  the  presence  of  the 
reducing  influence  of  the  carbon.  A  slag  cannot  be  an  efficient 
carrier  of  phosphorus  during  the  elimination  of  carbon  at  a  high 
temperature  if  the  acid  content  is  much  in  excess  of  25  per  cent, 
of  the  slag.  The  percentage  of  P2O5  that  can  be  carried,  there- 
fore, varies  inversely  as  the  percentage  of  SiO2  present.  The 
final  composition  of  a  good  basic  open  hearth  slag  will  be  approxi- 
mately as  follows: 

SiOo.  P.,05.  CaO  +  MgO.  FeO.  MnO. 

20  per  cent.  5  per  cent.  50  per  cent.  15  per  cent.  10  per  cent. 

The  necessity  of  limiting  the  SiO2  in  the  slag  so  rigidly  makes 
it  imperative  that  silicon  should  be  kept  low  in  the  pig  iron.  Since 
the  percentage  of  SiCX  must  be  so  low  in  the  slag,  any  increase 
of  silicon  in  the  pig  means  an  increase  of  several  times  as  much 
basic  material,  as  well  as  the  loss  of  an  equivalent  quantity  of  iron. 
The  silicon  in  basic  pig  iron  is,  therefore,  not  only  a  dead  loss  to 
the  purchaser,  but  entails  the  consumption  of  considerable  other 
material  which  must  also  be  purchased. 

Composition  of  Pig — The  presence  of  manganese  is  of  no 
especial  advantage  to  basic  pig  iron.  As  a  source  of  basicity  its 
oxides  are  too  unstable  to  be  effective  in  eliminating  phosphorus, 
although  its  affinity  for  sulphur  may  assist  in  the  removal  of  that 
element.  Owing  to  the  basicity  of  the  slag,  manganese  is  not  so 
•readily  taken  up  by  it  in  this  process  as  in  the  acid  processes,  and 
its  elimination  may  therefore  be  incomplete,  which  may  result  in 
too  high  manganese  in  the  finished  product  after  recarburization. 
It  is  best,  therefore,  to  limit  it  also. 

While  the  elimination  of  phosphorus  in  this  process  may  be 
practically  complete,  yet  it  is  accomplished  only  at  considerable 
expenditure  of  basic  reagents.  We  have  seen  that  each  pound  of 
phosphorus  needs  several  pounds  of  such  reagents.  It  should 
therefore  be  kept  low,  as  the  cost  of  extraction  multiplies  rapidly. 
As  a  large  portion  of  it  is  oxidized  during  melting,  it  does  not 
yield  its  equivalent  of  iron  to  the  bath.  That  portion,  however, 


304  Blast  Furnace. 

which  is  oxidized  by  the  iron  in  accordance  with  the  following 
reaction, 

3P2  +  5Fe203  -  5Fc2  +  3P205, 

yields  3  pounds  of  iron  for  each  pound  of  P  oxidized. 

Owing  to  the  fact  that  a  considerable  percentage  of  sulphur 
is  taken  up  by  a  basic  slag,  it  is  not  necessary  that  sulphur  should 
be  so  strictly  limited  in  basic  pig  as  in  acid  irons.  Usually  50 
per  cent,  and  often  75  per  cent,  of  the  sulphur  in  the  pig  can  be 
extracted.  A  basic  slag  also  prevents  transmission  of  sulphur 
from  the  gases  to  the  metal  by  assimilating  it  during  its  passage. 

As  in  the  other  processes,  carbon  is  the  last  element  to  be 
oxidized.  The  removal  of  the  residual  carbon  is  effected  by  the 
oxidizing  effect  of  lumps  of  ore  thrown  into  the  bath.  The  reac- 
tion causes  an  evolution  of  CO,  as  in  the  following  reaction, 

3C  +  Fe203  =  3CO  +  2Fe. 

which  agitates  the  bath,  exposing  it  to  the  action  of  the  slag  and 
flame.  At  the  same  time  the  carbon  reduces  an  equivalent  of  iron 
equal  to  3  pounds  per  pound  of  carbon  oxidized. 

The  final  composition  of  basic  open  hearth  steel  usually  falls 
within  these  limits : 

C.  Si.  Mn.  P.  S.  Fe. 

Per  cent.         Per  cent.  Per  cent.  Per  cent.  Per  cent.  Per  cent. 

0.05-1.5  Tr.-0.2  0.3-0.7  0.005-0.05  0.02-0.06  99.5-98.0 

THE     BASIC     BESSEMER     PROCESS. 

Operation. — The  basic-Bessemer  or  Thomas-Gilchrist  process, 
which  was  first  applied  in  1878,  is  a  pneumatic  process,  carried 
on  in  a  vessel  differing  from  the  Bessemer  converter  only  in  the 
character  of  its  lining.  The  process  was  designed  to  supplement 
the  power  of  the  Bessemer  process  to  eliminate  rapidly  and 
cheaply  •  the  silicon,  manganese  and  carbon,  by  including  the 
elimination  of  phosphorus  and  sulphur.  As  we  have  seen,  this 
action  demands  a  slag  of  pronounced  basicity,  which  can  be  main- 
tained only  when  the  vessel  lining  is  of  basic  character.  The 
lining  is  usually  made  of  dolomite  which  has  been  thoroughly  cal- 
cined and  mixed  with  a  suitable  binder,  such  as  anhydrous  tar. 
The  vessel  is  charged  with  molten  pig,  turned  up,  and  blown  with 
an  air  blast  similar  to  the  Bessemer  process. 


Uses  of  Pig  Iron.  305 

Elimination  of  Metalloids — The  first  elements  to  oxidize 
are,  as  usual,  silicon  and  manganese.  They  unite  to  form  a  slag, 
which  is  of  insufficient  basicity  to  spare  the  dolomitic  lining  of  the 
vessel.  It  is  therefore  customary  to  charge  the  converter  before 
beginning  the  blow,  with  enough  burnt  lime  to  form  a  slag  with 
all  the  other  slag-making  materials  present,  which  shall  contain 
about  50  per  cent.  CaO  -j-  MgO.  This  serves  to  prevent  excessive 
corrosion  of  the  lining.  Generally  the  removal  of  silicon  and 
manganese  is  complete  at  the  end  of  six  to  seven  minutes,  and  the 
carbon  is  eliminated  at  the  end  of  twelve  to  fifteen.  While  phos- 
phorus is  oxidized  during  these  periods,  yet  the  oxide  is  not  stable 
in  the  presence  of  the  active  carbon  and  therefore  practically  none 
is  eliminated  until  the  carbon  is  gone.  It  usually  takes  three  to  five 
minutes  additional  blowing  to  remove  the  phosphorus.  Incident- 
ally, about  half  the  sulphur  is  removed  at  the  same  time. 

The  final  composition  of  steel  made  by  this  process  is  never 
as  low  in  phosphorus  as  at  the  end  of  the  blow,  because  the  reac- 
tions accompanying  recarburization  generally  reduce  again  a 
small  portion  of  the  oxidized  phosphorus  to  the  elemental  condi- 
tion. 

Composition  of  Pig — The  presence  of  silicon  in  this  process 
offers  the  same  disadvantages  that  we  have  seen  in  the  basic  open 
hearth  operation.  The  more  silicon,  the  more  basic  additions  are 
needed  to  neutralize  it  and  give  a  slag  sufficiently  basic  to  hold 
phosphorus  and  sulphur.  On  the  other  hand  a  certain  percentage 
of  silicon  is  desired  to  raise  the  temperature  of  the  heat  to  the 
ignition  point  of  carbon. 

Manganese,  being  of  basic  nature,  serves  to  neutralize  the  silica 
and  at  the  same  time  renders  the  slag  more  fusible. 

The  presence  of  phosphorus  is  the  essential  evil  which  makes 
the  process  necessary.  The  necessity  for  keeping  silicon  low  in 
the  pig  in  order  that  the  slag  may  be  sufficiently  basic  to  take  care 
of  the  phosphorus,  throws  upon  phosphorus  a  duty  which  is  per- 
formed by  silicon  in  the  acid  converter.  The  phosphorus,  since  it 
is  a  heat  producer  second  only  to  silicon,  serves  to  supply  the  defi- 
ciency of  heat  which  naturally  results  from  the  absence  of  consid- 
erable silicon. 

As  there  is  no  compensatory  reduction  of  iron,  as  in  the  case  of 


306  Blast  Furnace. 

purification  by  fixed  oxygen,  each  element  which  is  in  excess  of 
the  requirements  of  the  method  is  a  total  loss  to  the  purchaser, 
even  if  it  offers  no  especial  disadvantages  to  the  operation. 

The  final  composition  of  basic-Bessemer  steel  usually  falls  be- 
tween these  limits : 

C.  Si.  Mn.  P.  S.  Fo. 

Percent.  Percent.  Percent.  Percent.  Percent.  Percent. 

0.05-1.5  Tr.-O.O'J  0.4-0.5  0.05-0.15  0.04-0.08  99.5-98.0 

Chronology  of  Conversion  Methods. — Although  cast  iron 
in  the  form  of  pig  iron  is  now  the  starting  point  of  the  manufac-  • 
ture  of  all  other  ferrous  products,  its  attainment  to  this  distinction 
is  of  very  recent  date,  and  in  metallurgical  chronology,  the  blast 
furnace  is  a  comparatively  modern  institution.  The  production 
of  wrought  iron  direct  from  iron  ores,  and  the  manufacture  of 
steel  by  causing  bars  of  iron  to  absorb  carbon  through  contact 
with  charcoal  at  red  heat,  are  industries  whose  origins  are  lost  in 
antiquity.  For  many  centuries  wrought  iron  was  produced  by 
heating  ore  with  charcoal  and  a  small  blast  in  low  hearths,  or 
hollows  in  the  earth,  known  as  the  Catalan  forge.  During  the 
middle  ages  these  hearths  developed  under  ambitious  managers 
into  low  masonry  furnaces,  with  removable  fronts  for  extracting 
the  "  loup  "  or  lumps  of  iron.  As  furnaces  became  higher  and 
reducing  conditions  stronger,  the  furnacemen  were  annoyed  to 
find  that  a  portion  of  their  product  was  in  a  molten  state,  and  that 
on  solidifying  it  did  not  become  tough  and  strong,  but  was  com- 
paratively brittle.  This  new  material  afterwards  found  a  limited 
application  in  making  castings,  and  the  above  method  of  making 
wrought  iron  continued  for  some  time  longer.  Subsequently 
methods  were  devised  for  refining  the  cast  iron,  which  eventually 
displaced  the  production  of  wrought  iron  direct  from  the  ores. 
The  earlier  methods  of  refining  consisted  in  melting  the  cast  iron 
in  small  quantities  in  small  rectangular  hearths  by  means  of  char- 
coal and  a  blast  which  oxidized  the  metalloids.  The  method  was 
wasteful  and  the  fuel  expensive.  The  puddling  process,  which 
was  introduced  by  Henry  Cort  in  1784,  was  considered  a  great 
improvement,  because  the  metal  did  not  come  in  contact  with  the 
fuel  and  an  inferior  grade  could  be  used  in  consequence.  But  the 
hearth  was  made  of  sand,  and  as  there  was  no  compensatory  re- 


Uses  of  Pig  Iron.  307 

duction,  the  losses  were  large.     The  present  modification  was  in- 
troduced by  Hall  in  the  thirties. 

It  was  not  until  1856  that  a  method  was  developed  for  using 
pig  iron  in  producing  steel  direct.  In  that  year  Bessemer  dis- 
covered, in  England,  that  the  metalloids  can  be  eliminated  from 
molten  pig  iron  simply  by  blowing  through  it  a  current  of  at- 
mospheric air.  The  discovery  was  the  result  of  an  endeavor  to 
find  a  shorter  method  of  making  wrought  iron.  The  product, 
while  ostensibly  wrought  iron,  would  not  roll  without  crumbling, 
owing  to  the  admixture  of  oxidized  particles  of  iron.  It  was  ob- 
served by  Mushet  that  the  addition  of  a  small  percentage  of  metal- 
lic manganese  removed  the  oxygen  and  gave  the  metal  the  mal- 
leable quality  which  is  so  familiar  in  mild  steel.  The  basic  modi- 
fication of  this  process  was  also  brought  out  in  England  during 
the  seventies. 

Meanwhile,  during  the  sixties,  the  acid  open  hearth  method 
was  developed  by  Martin  of  France,  who  adapted  the  regenerative 
furnace  of  Siemens  to  melting  pig  iron  and  scrap  iron,  thereby 
introducing  a  new  method  of  steel  making,  still  sometimes  known 
as  the  Siemens-Martin  process,  although  the  process  has  since 
been  somewhat  modified  by  the  use  of  iron  ore.  The  use  of  a  basic 
hearth  was  adopted  on  the  Continent  some  years  later. 

NON-CONVERSION  IRONS. 

Of  the  irons  which  do  not  undergo  complete  conversion  during 
preparation  for  further  use  we  may  distinguish  two  classes,  those 
which  undergo  a  partial  change  in  composition  in  making  mallea- 
ble or  toughened  castings,  and  those  which  are  used  practically 
unchanged  in  making  gray  iron  castings.  The  latter  class  includes 
all  the  so-called  foundry  grades  of  iron. 

GRAY   IRON    CASTINGS. 

The  first  use  of  gray  pig  iron  to  make  castings  is  of  uncertain 
date,  but  probably  was  previous  to  1500  A.  D.,  since  cast  iron 
cannon  are  known  to  have  been  in  use  at  about  that  time.  Before 
its  introduction,  all  articles  of  iron  were  made  of  wrought  iron 
by  the  laborious  process  of  forging  and  welding.  The  building  up 
of  complicated  shapes  in  that  way  is  slow  and  expensive,  and 


308  Blast  Furnace. 

therefore  the  invention  of  a  modification  of  iron  which  was  suita- 
ble for  many  purposes  and  yet  could  be  melted  and  poured  di- 
rectly into  complicated  shapes  was  very  welcome.  In  spite  of 
the  cheapened  methods  of  producing  wrought  iron  and  steel,  and 
the  recent  introduction  of  steel  castings,  iron  castings  still  fill'a 
very  wide  field  of  usefulness,  and  must  continue  to  do  so,  not 
only  on  account  of  their  IOWT  cost  of  production,  but  also  because 
the  metal  is  better  suited  to  some  uses  than  either  wrought  iron 
or  steel. 

Grading  Foundry  Iron. — It  was  long  the  custom  to  grade 
pig  iron  for  its  various  uses  according  to  the  character  of  its  frac- 
tured surface.  The  different  grades  were  usually  designated  by 
numerals,  as  follows: 

1  X. — Open  grain,  having  large  crystals  of  graphite  to  the 
very  edge. 

2  X. — Slightly  closer  grain  with  a  markedly  closer  border. 
2  Plain. — Closer  than  2  X,  especially  toward  the  bottom. 
3. — Uniformly  closer  than  2  Plain. 

It  is  now  fast  becoming  customary  to  buy  iron  on  its  analysis 
instead  of  its  fracture,  and  the  interpretation  of  these  grade  num- 
bers in  terms  of  composition  is,  according  to  the  Warwick  Iron 
Co.,  as  follows: 

Grade.                           Si.               T.  C.  C.  C.  Mn.                 P.                      S. 

"Analyses    1X 2.0-3.0  3.5-4.0  0.1-0.3  0.4-0.6  0.4-0.5  0.01-0.03 

Pig  Iron,"     2  X 2.0-3.0  3.5-4.0  0.2-0.4  0-4-0.6  0.4-0.5  0.02-0.04 

S.R.  Church,     2  plain 2.0-3.0  3.5-4.0  0.20.5  0.4-0.6  0.4-0.5  0.02-0.06 

3    1.0-1.75  0.4-0.6  0.4-0.5  0.04-0.08 

A  more  elaborate  classification  which  has  grown  up  in  the 
South  to  meet  local  conditions  is  illustrated  by  the  analytical  limits 
of  the  Alabama  Consolidated  Coal  and  Iron  Co.'s  products. 

Grade.                              Si.             G.  C.  C.  C.              Mn.              P.                     S. 

Silvery    4.0-6.0     2.25-3.5  0.35-0.50  0.75-1.0  0.17-0.30  0.015-0.030 

No.  2  soft 3.0-4.5     2.25-3.5  0.35-0.50  0.75-1.250.20-0.30  0.020-0.030 

No.  1  soft 3.0  -3.8     2.25-3.5  0.35-0.50  0.75-1.25  0.20-0.30  0.020-0.025 

Ibi£     No.  1  foundry 2.5-2.752.25-3.5  0.35-0.50          1.10            0.30                 0.030 

No.  2  foundry 2.25-2.5     2.25-3.5  0.35-0.50          1.25            0.35                 0.035 

No.  3  foundry 2.0  -2.25   2.25-3.5  0.35-0.50          1.30            0.40                 0.040 

No.  4  foundry 1.75-2.0     2.25-3.5  0.35-0.50          1.35            0.45                 0.040 

The  physical  character  of  pig  iron  is  dependent  mainly  upon 
the  condition  of  the  carbon,  and  the  most  potent  factor  in  deter- 
mining the  condition  of  the  carbon  is  the  quantity  of  silicon  pres- 


Uses  of  Pig  Iron.  309 

ent.  Since  silicon  is  not  the  only  controlling  influence,  it  fre- 
quently happens  that  it  does  not  exert  its  normal  influence  on  the 
carbon,  whereupon  the  fracture  ceases  to  be  a  reliable  guide  to 
the  quantity  of  silicon  and  hence  to  the  quality  of  casting  that 
will  result.  It  is  now  more  usual,  therefore,  to  grade  the  iron 
according  to  its  silicon  content  rather  than  according  to  the  ap- 
pearance of  the  fracture. 

A  given  make  of  iron  frequently  fails  to  run  uniformly  in  qual- 
ity and  the  consequent  variation  might  cause  trouble  for  a  given 
class  of  work.  To  get  best  results,  therefore,  it  is  customary  to 
mix  several  makes  or  "  brands  "  of  a  given  grade,  rather  than  to 
risk  all  results  on  a  single  brand  with  its  liability  to  variation. 
Accidents  are  less  likely,  however,  when  iron  is  bought  strictly  on 
analysis. 

Properties  of  Foundry  Irons — The  wide  variation  in  the 
properties  of  cast  iron  permits  its  application  to  a  great  variety 
of  uses.  The  particular  qualities  which  adapt  it  to  making  cast-- 
ings are  its  ready  fusibility  and  low  shrinkage.  These  qualities 
are  directly  attributable  to  the  quantity  and  condition  of  the  car- 
bon present.  As  previously  stated,  the  quantity  of  carbon  in  pig 
iron  is  fairly  constant,  but  its  condition  in  castings  is  subject  to 
wide  variations.  There  are  four  chief  factors  which  affect  the 
condition  of  the  carbon,  viz. :  The  quantity  of  carbon  present ;  the 
initial  temperature  of  the  metal ;  the  rate  of  cooling ;  the  presence 
of  other  elements.  The  effects  of  these  various  factors  upon  the 
properties  of  cast  iron  may  be  conveniently  summarized  in  the 
following  table : 


bo  •  S  ^  «         's! 

M  "       £       2  2      « 

«•       3       "S       -S  fe      S 

I  -   1     J    -  |      I      ^       ^-       I      1 

oQOfao:woa't-5K 


Total  C  * 
Comb.  C  
Graph.  C  * 
Si  O 
Mn  ...  .  .  .  .  O 

ii 

[] 

o 
o 
o 
o     i 

P  

S 

* 

Slow  cooling.  * 
Rapid  cooling.  . 

•; 

* 

O  =  small  percentages, 
f  ]  —  large  percentages. 
*  ~  all  percentages. 


310  Blast  Furnace. 

PURCHASE   SPECIFICATIONS    FOR    FOUNDRY    IRONS. 

The  standard  purchase  specifications  for  pig  iron  adopted  by 
the  American  Society  for  Testing  Materials  is  as  follows : 

1.  All  purchases  to  be  made  on  analysis. 

2.  Each  carload  to  be  considered  a  unit,  one  pig  from  each 
four  tons  to  constitute  a  sample.     Drillings  taken  from  fractures 

Am  soc  °f  P*£s  to  fairbr  represent  the  pig  and  an  equal  quantity  from  each 
pig  mixed  thoroughly  and  ground  before  analysing.  In  case  of 
dispute  an  independent  analysis  to  be  made  on  one  pig  for  each 
two  tons,  the  cost  to  be  borne  by  the  party  in  error. 

3.  All  contracts,  unless  otherwise  agreed,  to  allow  a  variation 
of  10  per  cent.  Si  either  way  and  0.02  S  above  the  standard  for 
the  given  grade.    A  deficiency  of  silicon  between  10  per  cent,  and 
20  per  cent.,  subject  to  4  per  cent,  deduction  in  price. 

4.  In  absence  of  other  agreements  the  following  analyses  rep- 
resent standard  grades  of  foundry  irons : 

Volumetric.  Gravimetric. 

Per  cent.  Si.              Per  cent.  S.  Per  cent.  S. 

No.   1 2.7",                            0.03.",  0.045 

No.   2 2.2".                            0.045  0.055 

No.   3 1.75                            0.055  0.065 

No.   4 1 .25                            O.OG5  0.075 

In  general  it  may  be  stated  that  for  average  foundry  irons  the 
following  rules  hold  good  : 

To  increase  strength  of  castings :  Decrease  phosphorus  and 
lessen  graphite  by  decreasing  silicon,  thereby  allowing  more  com- 
bined carbon.  The  manganese  may  also  be  increased  and  the 
castings  cooled  more  rapidly. 

To  decrease  hardness  and  shrinkage  of  castings :  Decrease 
sulphur  and  combined  carbon  and  increase  the  quantity  of  graphite 
fphur  and  combined  carbon  and  increase  the  quantity  of  graphite 
through  the  addition  of  silicon  or  by  cooling  more  slowly. 

To  prevent  chilling  of  castings:  Decrease  sulphur  and  man- 
ganese and  increase  silicon  and  slow  cooling. 

To  prevent  blowholes  in  castings:  Decrease  sulphur  and  in- 
crease manganese  and  silicon. 

To  prevent  kish:  Decrease  the  percentage  of  carbon  by  add- 
ing scrap  to  the  cupola. 

The  addition  of  small  quantities  of  ground  ferromanganese 


Uses  of  Pig  Iron. 


311 


p.  1149. 


or  50  per  cent,  ferrosilicon  in  the  ladle  gives  generally  beneficial 
results.  It  deoxidizes  the  metal,  thereby  softening  and  strengthen-   Nov."ifi906, 
ing  it,  decreasing  shrinkage  and  making  clean  castings  without 
materially  altering  the  composition  of  the  metal. 

Pig  iron  which  shows  no  tendency  to  vicious  properties  such  as 
hardness,  weakness,  shrinkage,  etc.,  is  sometimes  termed  "  neu- 
tral "  pig. 

In  order  to  illustrate  the  type  of  metal  that  is  suited  to  castings 
of  different  degrees  of  hardness,  the  specifications  of  the  Case 
Threshing  Machine  Company  will  serve  as  an  example : 


Soft  castings, 
pulleys  or 

small  castings. 

Si    2.20-2.80 

S    below  0.085 

P   below  0.70 

Mn below  0.70 

Tensile  strength  per  square  inch 18,000  Ib. 

Transverse  strength  per  square  inch ....    2,000  Ib. 

Deflection,  not  less  than 0.10  in. 

Shrinkage,  per  foot,  not  over 0.127  in. 

Chill,   not   over 0.05  in. 


Hard 

castings, 

Medium  castings 

,       valves 

cylinders,  gears, 

and  H.  P. 

pinions,  etc. 

cylinders. 

1.40-2.00 

1.20-1.60 

below  0.085 

below  0.095 

Iron  Age, 

below  0.70 

below  0.70 

Sept.  29,  1898, 

below  0.70 

below  0.70 

pp.  4,  5. 

20,000  Ib. 

22,000  Ib. 

2,200lb. 

2,400  Ib. 

0.09  in. 

0.08  in. 

0.1  36  in. 

0.148  in. 

0.15  in. 

0.25  in. 

The  decrease  of  silicon  is  accompanied  by  an  increase  of  com- 
bined carbon,  which  effects  the  increase  of  strength  and  stiffness 
of  the  metal.  As  the  shrinkage  generally  varies  with  the  hardness 
of  cast  iron,  it  becomes  a  valuable  indication  of  the  quality  of  iron, 
since  it  is  measured  with  comparatively  little  trouble.  Shrinkage 
is  usually  reckoned  to  be  about  J/s  inch  to  a  foot,  but  it  is  variable 
and  depends  upon  the  silicon  content  anj  area  of  section,  as  indi- 
cated by  the  following  table : 

x  y2  in.    1  x  1  in.     1  x  2  in.    2  x  2  in.     3  x  3  in.  4  x  4  in. 


1  per  c«it 0.183  0.158  0.146  0.130  0.113 

2  per   cent 0.159  0.133  0.121  0.104  0.085 

3  per   cent 0.135  0.108  0.095  0.077  0.059 

Surface 

Ratio—         — 0.125  0.250  '0.333  0.500  0.750 

Volume 


0.102 

0  074  Keep's 

r'rV!  "Cast  Iron," 

0.045  p.  155. 

1.000 


The  class  of  iron  that  is  suited  to  certain  uses  may  be  illus- 
trated by  the  composition  of  the  samples  used  by  the  Committee 
on  Standardizing  Testing  of  Cast  Iron. 


312  Blast  Furnace. 

Class  of  work.  Si.  P.  S. 

Novelties 4.19  1.236  0.080 

Stove  plate .3.19  1.160  0.084 

Cvlindprs    --4i)  °-8:™  0.084 

Assoc.,    Light    machinery 2.04  0.578  0.044 

X,  part  II,     Heavy  machinery 1.96  0.522  0.081 

Dynamo  frames 1.95  0.405  0.042 

Ingot  molds 1.67  0.095  0.032 

Car  wheels 0.97  0.301  0.060 

Chilled   roll 0.85  0.482  0.070 

Sand  roll 0.72  0.454  0.070 

Effects  of  Size  of  Castings — As  the  size  of  a  casting 
exerts  a  marked  influence  upon  its  rate  of  cooling,  it  follows  that 
composition  should  vary  with  the  size  of  casting.  Since  a  thin 
section  cools  rapidly,  it  should  be  made  of  iron  which  is  very 
fluid  and  has  no  tendency  to  chill.  On  the  other  hand,  a  large 
mass  of  metal  which  cools  slowly  should  not  be  allowed  to  form 
large  crystals  of  graphite  in  its  interior.  In  general  it  may  be 
said  that  small  castings  should  be  high  in  Si  and  P,  while  large 
ones  should  be  high  in  Mn  and  S.  The  following  limits  of  com- 
position, based-on  size  of  castings,  have  been  suggested: 

Thickness  of  section.                                  Si.  P.  Mn.                    S. 

Under  %  inch  thick 3.25  1.00  0.40  0.025 

V4  to  %  inch  thick 2.75  0.80  0.40  0.040 

%  to  %  inch  thick 2.50  0.75  0.50  0.050 

Iron  Age,    %  to  1  inch  thick 2.00  0.70  0.60  0.060 

Feb.  15, 1906J     i  to  l1/^  inches  thick 1.75  0.65  0.70  0.070 

P.  589.    1%  to  2  inches  thick 1 .50  0.60  0.80  0.080 

2  to  2%  inches  thick 1 .25  0.55  0.90  0.090 

2%  to  3  inches  thick 1.00  0.50  1.00  0.100 

As  a  rule,  cast  iron  is  not  required  to  stand  a  transverse  strain 
of  over  2500  pounds  per  square  inch.  Generally  small  sections 
are  not  made  for  strength,  and  are  therefore  ample  for  the  de- 
mands. Unsymmetrical*  castings  may  be  benefited  by  exposing 
the  larerer  sections  to  cool  first. 

o 

Effect  of  Shape  of  Castings. — Since  cast  iron  during 
solidification  tends  to  build  up  a  crystalline  structure  whicft  grows 
in  directions  perpendicular  to  the  cooling  surfaces  it  follows  that 
a  plane  of  weakness  will  develop  at  every  sharp  angle,  thus : 


Uses  of  Pig  Iron.  313 

For  this  reason  care  should 'be  exercised  to  have  no  abrupt 
changes  of  direction  in  patterns,  but  well  rounded  corners,  thus : 


in  order  that  no  distinct  plane  of  cleavage  may  develop  during 
solidification. 

Remelting. — In  making  castings  from  any  metal  it  is  nec- 
essary that  the  metal  should  be  in  a  thoroughly  liquified  condition 
in  order  that  it  may  reach  all  parts  of  the  mould  uniformly.  If 
a  blast  furnace  could  be  run  with  such  regularity  as  to  turn  out 
iron  of  a  tolerably  constant  composition,  it  would  be  economy  to 
run  foundries  in  connection  with  blast  furnace  plants.  Certain 
plain,  heavy  castings  are  made  at  every  furnace  plant  at  times,  but 
no  foundries  in  this  country  are  run  on  direct  blast  furnace  metal 
In  England  the  attempt  has  been  made  to  operate  in  this  manner  IronAge, 
to  produce  heavy  work,  by  using  carefully  selected  materials  and  Jau-12'19< 
carefully  regulated  temperatures  in  the  furnace.  In  this  country, 
however,  it  is  the  universal  custom  to  remelt  the  pig  iron  in  cupola 
furnaces  and  pour  the  remelt  into  the  moulds. 

Operation  of  Cupola — The  cupola  furnace  is  a  cylindrical, 
riveted,  plate  affair,  lined  with  firebricks  and  pierced  near  the  bot- 
tom for  tuyeres.  It  is  usually  about  10  feet  high  and  varies  in 
diameter  up  to  8  or  10  feet,  according  to  capacity  required.  The 
cupola  charge  usually  consists  of  a  bed  of  coke  of  1000  to  2000 
pounds,  according  to  the  size  of  the  cupola.  Upon  this  3000  to 
6000  pounds  of  iron  are  charged.  Subsequent  charges  are  usual- 
ly smaller,  ranging  from  400  to  4000  pounds  of  iron  and  a  gradu- 
ally decreasing  proportion  of  fuel.  The  usual  fuel  ratios  are  i 
pound  of  coke  to  7  to  10  pounds  of  iron.  A  small  percentage  of 
limestone  is  generally  charged  to  flux  the  fuel  ash,  and  any  sand 
which  may  adhere  to  the  pigs.  A  vigorous  combustion  is  main- 
tained by  a  blast  of  air  at  atmospheric  temperature,  forced  through 
the  tuyeres  at  a  low  pressure,  usually  10  to  20  ounces  per  square 
inch.  The  blast  may  be  propelled  either  by  a  fan  blower,  such  as 


314  Blast  Furnace. 

the  Sturtevant,  or  a  positive  blower  like  the  Connorsville.  Ordi- 
narily the  positive  blower  will  furnish  blast  at  a  higher  pressure 
with  less  expenditure  of  power  per  ton  than  the  fan  blower,  and 
the  rate  .of  melting  is  proportionately  higher.  At  low  pressures, 
however,  the  fan  blower  is  more  flexible  and  furnishes  a  more 
uniform  blast. 

Rate  of  Melting.  —  The  melting  zone  of  the  cupola  depends 
for  its  position  upon  the  force  of  the  blast.  A  light  blast  will  burn 
the  coke  near  the  tuyeres.  A  high  pressure  blast  drives  the  zone 
of  combustion  higher.  Usually  a  pressure  which  melts  at  about 
1  8  inches  above  the  tuyeres  is  considered  best. 

The  rate  of  melting  will  depend  upon  the  fuel  ratio  and  the 
rate  of  combustion.  The  rate  of  combustion  is  accelerated  by 
pressure  of  blast  but  is  always  in  proportion  to  the  quantity  of 
air  blown.  The  quantity  of  air  varies  as  the  square  root  of  the 
pressure,  and  bears  a  tolerably  definite  ratio  to  the  quantity  of 

CO 

fuel.     Generally  the  ratio  -™-  in  the  escaping  gases  is  about  I, 


from  which  it  is  easy  to  see  that  each  pound  of  coke  needs  7.3 
pounds,  or  105  cubic  feet  of  air  at  60  degrees  F.  From  this  it  is 
evident  that 

A  melting  ratio  of  6  requires  39,200  cubic  feet  air  per  ton  pig. 
A  melting  ratio  of  7  requires  33,600  cubic  feet  air  per  ton  pig. 
A  melting  ratio  of  8  requires  29,400  cubic  feet  air  per  ton  pig. 
A  melting  ratio  of  3  requires  26.100  cubic  feet  air  per  ton  pig. 
A  melting  ratio  of  10  requires  23,500  cubic  feet  air  per  ton  pig. 

The  rate  of  melting  also  varies  with  the  size  of  the  cupola.  The 
pressure  required,  and,  consequently,  the  rate  of  melting,  will 
rise  as  the  diameter  of  the  cupola  increases.  Generally  it  may  be 
said  that  a 

30-inch  cupola  requires    8  ounces  pressure  and  will  melt    2-  3  tons  per  hour. 

45-inch  cupola  requires  10  ounces  pressure  and  will  melt     6-  1  tons  per  hour. 

Nov.  30,  1905^         60-inch  cupola  requires  12  ounces  pressure  and  will  melt  10-12  tons  per  hour. 

P.  451.         72-inch  cupola  requires  11  ounces  pressure  and  will  melt  16-18  tons  per  hour. 

84-inch  cupola  requires  16  ounces  pressure  and  will  melt  21-24  tons  per  hour. 

It  appears  from  this,  that  each  square  foot  of  cupola  area 
melts  0.5  to  0.6  tons  pig  per  hour,  and  the  pressure  in  ounces 
should  approximate  the  square  root  of  three  times  the  cupola 
diameter  in  inches.  Usually  0*00045  H.  P.  will  deliver  I 
cubic  foot  of  air  per  minute  at  I  ounce  pressure.  With  cen- 


Uses  of  Pig  Iron.  315 

trifugal  fans,  the  melting  capacity  of  the  cupola  is  nearly  pro- 
portional to  the  speed  of  the  fan,  the  pressure  is  nearly  proper-   jSfeiv 
tional  to  the  square  of  the  speed,  and  the   H.   P.   used  is  ap- 
proximately proportional  to  the  cube  of  the  speed. 

The  use  of  a  central  tuyere  in  the  bottom  of  a  cupola  in  con- 
junction with  the  usual  tuyeres  tends  to  make  combustion  more   iu8t.  Jour 
complete,   thereby  saving   fuel  and  increasing  the  melting  rate,   p.2«.' 
but  it  is  difficult  to  maintain,  owing  to  its  exposed  position. 

Changes  in  Composition — While  the  remelting  of  iron 
in  the  cupola  is  not  intended  to  affect  its  composition  and  proper- 
ties, as  a  matter  of  fact  it  rarely  yields  an  unchanged  metal  and 
sometimes  the  alteration  may  be  considerable. 

The  factors  which  conspire  to  alter  the  composition  of  the 
iron  during  melting  are  two :  the  blast  and  the  fuel.  The  former 
tends  to  remove  some  elements  through  oxidation,  while  the  latter 
tends  to  add  some  through  absorption.  Silicon  and  manganese, 
being  readily  oxidized,  are  invariably  lessened  during  remelting, 
the  degree  of  change  being  governed  by  the  time  that  the  metal 
is  exposed  to  the  action  of  the  blast.  Sulphur  and  phosphorus  En 
are  usually  absorbed  from  the  fuel,  the  amount  depending  upon  p-  46 
the  quantity  of  fuel  and  its  purity.  Carbon  in  the  metal  may  in- 
crease or  decrease  according  to  the  influence  to  which  the  metal 
is  most  exposed. 

The  actions  of  silicon  and  manganese  during  remelting  follow 
each  other  closely  and  vary  according  to  two  conditions,  viz.,  the 
quantity  of  the  elements  present  and  the  quantity  of  oxygen  to 
which  they  are  exposed.  If  the  percentage  of  these  elements  is 
high,  not  only  is  the  quantity  lost  larger  but  the  proportion  is 
higher.  For  example,  when  silicon  is  as  high  as  3  per  cent,  the 
loss  is  generally  more  than  10  per  cent,  of  that  present,  while 
when  only  %  per  cent,  is  present,  the  loss  may  be  scarcely  notice- 
able. Both  iron  and  carbon  have  a  protecting  influence  upon 
silicon  when  it  is  in  small  quantities. 

The  greater  the  quantity  of  blast  and  the  longer  the  metal  is 
exposed  to  it  the  more  oxidation  will  take  place,  and  the  greater 
will  be  the  loss  of  silicon  and  manganese.  For  this  reason,  the 
loss  by  oxidation  is  generally  greater  in  larger  cupolas.  The 
following  statement  represents  av.erage  results : 


316  Blast  Furnace. 

Cupola  diameter.                                                             Silicon  lost.  Manganese  lost. 

anTiwIi;    r»<ler  40  feet 10  per  cent.  15  per  cent. 

p.  20.    40   to  GO  feet 1  r>  per  cent.  20  per  cent. 

Over  60  feet 20  per  cent.  25  per  cent 

In  addition  to  loss  by  oxidation  manganese  may  be  carried  off 
by  combining-  with  sulphur  to  form  MnS,  which  enters  the  slag. 
The  loss  of  Mn  is  generally  greater  in  high  sulphur  irons.  When 
the  presence  of  manganese  is  desirable,  and  excessive  sulphur  is 
present  the  addition  of  l/2  per  cent,  of  ferromanganese  will  coun- 
teract this  tendency. 

The  absorption  of  phosphorus  by  pig  iron  during  remelting  in 
cupolas  is  never  very  great.  The  tendency  is  present,  but  the 
action  is  incomplete,  and,  as  a  rule,  the  percentage  of  phosphorus 
is  fairly  constant  during  remelting. 

With  sulphur,  however,  the  action  is  more  positive.  The 
source  of  sulphur  is  the  fuel,  and  the  tendency  to  absorption  is 
proportional  to  the  quantity  of  sulphur  present.  This  tendency 
is  counteracted  by  three  influences,  namely,  the  quantity  of  lime- 
stone used  as  flux,  the  temperature  of  the  cupola,  and  the  quantity 
of  manganese  present.  A  highly  sulphurous  iron  melted  in  the 
presence  of  considerable  metallic  manganese  may  even  lose  sul- 
phur. The  use  of  manganese  ore  for  this  purpose  is  not  effica- 
cious, because  sulphur  does  not  unite  readily  with  oxides  of  man- 
ov.9,i|W5l  ganese,  and  the  cupola  is  unable  to  reduce  the  metal.  The  use  of 
ferromanganese  in  the  ladle  is  said  to  remove  50  per  cent,  of  the 
sulphur  present. 

The  action  of  carbon  during  remelting  also  depend  upon  con- 
ditions, the  oxygen  of  the  blast  tending  to  eliminate  it  and  the 
coke  tending  to  add  it.  As  the  iron  passes  the  tuyeres,  the  ten- 
dency of  the  blast  is  to  oxidize  the  carbon.  This  tendency  is  more 
marked  if  the  carbon  is  plentiful,  the  exposure  severe  and  the  pro- 
tection of  silicon  and  carbon  insufficient.  On  the  other  hand, 
long  contact  of  molten  iron  with  coke  at  high  temperatures  facili- 
tates the  absorption  of  carbon  and  the  quantity  may  increase.  In 
general,  it  may  be  stated  that, 

Much  carbon,  little  Si  and  Mn,  much  blast  and  low  fuel  quan- 
tity tend  toward  decrease  of  carbon  content,  while 

Low  carbon,  much  Si  and  Mn,  light  blast  and  much  fuel  tend 
to  increase  carbon  content 


Uses  of  Pig  Iron.  317 

Effect  of  Fuel — Aside  from  its  impurities,  the  quantity  oi 
fuel  used  in  remelting  pig  iron  affects  the  composition  of  castings 
through  its  calorific  properties.  Rapidity  of  melting  tends  to 
lessen  the  period  of  oxidation,  and  gives  soft  castings.  Good  and 
sufficient  fuel  brings  down  the  iron  hot  and  fluid,  so  that  impuri- 
ties separate  well  and  the  moulds  are  well  filled.  For  these  rea- 
sons, selected  fuel  is  generally  used  in  the  form  of  72-hour  bee- 
hive coke.  The  use  of  by-product  coke  is  not  unusual,  comparison 
shows  that  it  is  capable  of  melting  iron  satisfactorily.  More- 
over, as  its  method  of  manufacture  involves  the  presence  of  a  iron  Age, 

.  .  .  Jan.  11,  1903; 

chemist,  it  is  possible  to  get  better  information  concerning  it  than  p-  is. 
in  the  case  of  beehive  coke.  Too  little  fuel  causes  slow  melting 
and  cold  iron,  permitting  much  oxidation  and  absorption  of  sul- 
phur, which  leads  to  hard  castings.  Good  fluxes  are  necessary  to 
free  the  iron  of  its  impurities  and  make  clean  and  smooth  cast- 
ings. 

Effect  of  Tuyeres — The  position  of  the  tuyeres  of  the  cu- 
pola is  not  without  its  effect  upon  remelting.  For  heavy  work 
it  is  necessary  to  have  them  high,  in  order  that  the  space  below 
may  be  a  sufficient  reservoir  for  the  quantity  of  iron  needed  for  a 
large  casting.  This  permits  long  contact  with  the  fuel,  and  hence 
absorption  of  both  carbon  and  sulphur,  which  is  not  detrimental 
to  heavy  work. 

A  cupola  with  low  tuyeres  must  be  drawn  frequently  and  hence 
is  suitable  only  for  light  work,  and  when  low  carbon  and  sulphur 
are  required. 

Action  of  White  Iron. — Gray  iron  melts  more  slowly  than 
white  iron,  and  needs  a  higher  temperature,  owing  to  the  neces- 
sity of  the  recombining  of  the  graphite,  but  when  it  is  melted  it 
is  usually  more  fluid  than  white  iron.  White  iron  becomes  some- 
what pasty  on  cooling,  and  entangles  gases,  causing  blowholes. 
White  iron  melts  as  low  as  2000  degrees  F.,  while  gray  iron  may 
require  more  than  2200  degrees  F.  In  general,  it  may  be  said  that 
the  higher  the  total  carbon,  the  lower  will  be  the  melting  point, 
and  the  more  fluid  the  iron.  Gray  iron  throws  off  a  layer  of 
graphite  on  solidification,  which  covers  the  surface  of  castings, 
and  prevents  them  sticking  to  the  sand,  thereby  giving  them  a 
smooth  appearance.  Owing  to  their  different  rates  of  melting, 


318  Blast  Furnace. 

gray  and  white  iron  do  not  give  uniform  results  when  melted  to- 
gether in  the  cupola.  Usually  the  white  iron  comes  down  first 
and  is  followed  by  the  gray  iron. 

CHILLED   CASTINGS. 

For  certain  purposes,  however,  such  as  the  formation  of  hard 
surfaces,  white  iron  is  very  desirable.  Castings  with  a  surface 
layer  of  white  iron  backed  by  gray  iron  are  known  as  chilled 
castings.  They  are  made  from  irons  low  in  silicon,  in  moulds 
having  a  metallic  surface  which  corresponds  to  the  surface  to  be 
chilled.  The  metallic  surface  conducts  the  heat  away  from  the 
casting  so  much  more  rapidly  than  sand  that  there  is  not  sufficient 
time  for  the  separation  of  graphite.  It  is  always  necessary  to 
use  an  iron  low  in  silicon  in  order  that  there  may  not  be  too  great 
an  initial  tendency  to  form  graphite.  It  is  difficult  to  chill  irons 
with  over  2  per  cent,  of  silicon.  The  presence  of  sulphur  and 
oxygen  increases  the  chilling  tendency.  It  is  said  that  o.oi  per 
cent,  sulphur  will  neutralize  the  softening  effect  of  o.i  per  cent, 
silicon.  The  addition  in  the  cupola  of  steel  scrap,  chilled  or  white 
iron  or  manganese  has  the  effect  of  deepening  the  chill.  A  man- 
ganese chill,  however,  is  undesirable  on  account  of  a  tendency  to 
"  spall."  With  average  sulphur  and  manganese  low,  silicon 
should  give  the  following  results : 

1.00  per  cent.  Si  gives  ys  inch  depth  of  chill. 
0.75  per  cent.  Si  gives  *4  inch  depth  of  chill. 
0.50  per  cent.  Si  gives  */2  inch  depth  of  chill. 
0.40  per  cent.  Si  gives  1  inch  depth  of  chill. 
0.30  per  cent.  Si  gives  1%  inch  depth  of  chill. 

If  sulphur  and  manganese  are  high,  the  chill  for  a  given  sili- 
con will  be  correspondingly  deeper.  The  addition  of  small  quan- 
tities of  ferromanganese  to  the  ladle  will  lessen  the  depth  of  chill, 
through  the  removal  of  sulphur  and  oxygen. 

Non-chilling  irons  may  be  used  in  .making  chilled  castings, 
either  by  mixture  with  chilling  irons,  in  the  cupola,  or  by  melting 
direct  in  the  air  furnace,  by  which  .the  composition  may  be  modi- 
fied through  oxidation  until  it  acquires  the  chilling  tendency. 
For  such  castings  the  air  furnace  has  some  advantage  over  the 
i906;  cupola;  the  content  of  silicon,  manganese  and  carbon  may  be 
'  regulated  more  exactly ;  the  tendency  to  absorb  sulphur  as  silicon 
decreases  is  less,  since  the  metal  is  not  in  contact  with  the  fuel ; 


Uses  of  Pig  Iron. 


319 


and  larger  quantities  of  metal  may  be  prepared  simultaneously. 
This  method  is  usually  employed  in  producing  chilled  rolls.  They 
are  usually  cast  on  end  with  the  body  in  chills  and  the  necks  in 
sand.  A  heavy  sinkhead  serves  to  supply  additional  metal  during 
contraction. 

Charcoal  pig  usually  shows  great  strength  and  a  tendency  to 
chill,  therefore  it  is  in  demand  for  making  carwheels,  which  re- 
quire great  strength  combined  with  a  very  hard,  durable  tread. 
The  composition  recommended  by  the  American  Society  for  Test- 
ing Materials  is  as  follows : 

Total  carbon 3.50  per  cent 

Si 0.70  per  cent. 

Mn  0.40  per  cent. 

I' 0.50  per  cent. 

S %. 0.08  per  cent. 

TOUGHENED  CASTINGS. 

Gray  iron  castings  rarely  give  over  2000  pounds  per  square  inch 
transverse  strength,  or  20,000  pounds  tensile  strength.  Owing  to 
demands  for  stronger  castings  for  use  in -high  pressure  cylinders, 
pumps,  etc.,  the  practice  of  melting  gray  iron  with  varying  per- 
centages of  mild  steel  or  wrought  scrap  has  been  adopted.  The 
resulting  metal  goes  under  the  name  of  **se mi-steel,"  although 
from  its  former  use  in  making  gun  carriages  it  is  sometimes 
known  as  "gun-iron"  The  use  of  20  to  30  per  cent,  scrap  will 
generally  increase  the  strength  by  at  least  30  per  cent,  through 
decreasing  graphitic  carbon,  and  strengths  of  over  3000  trans- 
verse and  30,000  tensile  are  the  rule.  .Such  metal  can  successfully 
replace  many  steel  castings.  Care  must  be  exercised  in  the  use 
of  scrap,  however.  Steel  increases  shrinkage ;  hard  steel  makes 
hard  spots ;  wrought  iron  increases  porosity ;  thick  castings  will 
stand  more  than  thin  ones.  The  effect  of  various  additions  is 
illustrated  in  the  following  table : 


Iron  Age, 
Apr.  23,  1903, 
p.  2. 


Tr.  Am.  Soc.s 
M.  E..XX, 
p.  615. 


Iron  Age, 
July  20,  19053 
p.  162. 


Per  cent. 

steel. 

Si. 

o 

1  96 

25  

.1.50 

0.  

1  76 

25  

.1.83 

12%  

.2.16 

25  ."...... 

.2.36 

0  

9  35 

37%.  . 

1.97 

Mn. 
0.44 
0.33 

0.53 
0.55 


0.56 
0.48 


P. 

0.446 

0.532 

0.488 
0.610 

0.315 
0.327 

0.515 
0.470 


S. 

0.104 
0.065 

0.062 
0.100 

0.060 
0.064 

0.061 
0.093 


c.  c. 

0.63 
0.64 

0.5.1 
0.51 

1.06 
1.08 

0.54 
0.57 


T.  C. 
3.18 
3.44 

3.12 
2.44 

2.30 
2.15 

3.40 
2.83 


Trans.  Per  ct.  Ten.  Per  ct. 
str.     incr.      str.    incr. 


2,230 
2,840 

2,440 
3,280 

2,670 
3,200 

2,200 
3,050 


85 


33 


21,950 
30,500 

22,180 
36,860 

26,310 
31,560 

21,990 
32,530 


40 


or, 


20 


5Q 


Eng'r  News, 
XLIX, 
p.  309. 


Iron  Age, 
June  19, 1902o 
p.  27. 


320  Blast  Furnace. 

EFFECTS  OF  MOULDING. 

The  production  of  good  castings  is  very  dependent,  also,  upon 
the  character  of  the  moulding  sand  and  the  arrangement  of  the 
moulds,  particularly  with  respect  to  the  proper  gateing  and  dis- 
tribution of  the  metal. 

The  essential  qualities  of  a  good  moulding  sand  are  toughness 
!  and  porosity.  The  sand  when  dampened  should  cohere  on  pres- 
sure and  retain  imprints  distinctly,  yet  should  be  porous  enough 
to  allow  escape  of  hot  air,  steam  and  gases. 

The  essential  constituents  of  moulding  sand  are :  Free  silica 
or  sand,  and  silicate  of  alumina  or  clay.  The  former  gives  porosi- 
ty ;  the  latter  strength.  Porosity  is  diminished  by  the  presence  of 
clay,  by  the  fineness  of  the  sand  and  by  the  regularity  of  the  shape 
of  the  grains.  The  finer  the  sand  the  better  the  surface  of  the 
castings.  The  strength  of  the  sand  should  vary  with  the  kind  of 
Mar?"  1906  wor^'  The  san<^  depends  for  its  strength  upon  the  properties  of 
P.  95i.'  the  clay  or  "  bond,"  the  shape  of  the  sand  grains  and  the  thorough- 
ness of  mixing.  Strength  may  be  supplemented  by  using  binding 
compounds,  or  by  the  use  of  nails  or  "  j aggers." 

Moulding  Sand. — Good  moulding  sand  will  usually  be 
found  to  have  a  composition  between  the  following  limits : 

SiO2 75-85  per  cent.  I  of  which  60-70  per  cent.  =  free  SiO2,  and  20-30 

V\12O3 7-10  per  cent.  J  per  cent.  =  clay  bond. 

Fe2O-  below 6  per  cent. 

CaO  below 2  per  cent. 

Alkalis  below.  .  .^  per  cent. 

The  sum  of  the  last  three  items  should  never  exceed  7  per  cent, 
as  they  would  seriously  interfere  with  the  refractoriness  of  the 
sand.  The  higher  the  percentages  of  pure  quartz  and  pure  clay, 
and  the  coarser  the  sand,  the  greater  will  be  the  refractoriness. 
Large  castings  require  sand  of  greater  refractoriness  than  small 
ones. 

Moulds. — Sand  moulds  may  be  roughly  classified  into  green 
sand,  dry  sand  and  loam  moulds. 

Green  sand  moulds  consist  of  moist  sand,  rammed  around  a 
pattern  in  wood  or  iron  "  flasks,"  which  receive  the  metal  direct. 

Dry  sand  moulds  differ  from  green  sand  only  in  the  fact 
E°nUgVsS!  tnat  the  mould  is  dried  at  a  moderate  temperature  for  24.  hours 
tii,p.2os.  kefore  use  They  are  much  firmer  than  green  sand,  and  hence 


Uses  of  Pig  Iron.  321 

are  used  for  larger  castings.  They  also  permit  the  use  of  higher 
temperatures,  which  is  favorable  to  fluidity  and  hence  cleaner 
metal. 

Loam  moulds  are  used  only  for  very  heavy  work.  Usually 
no  pattern  is  used,  but  the  loam  is  shaped  up  roughly  over  a 
backing  of  brick  on  the  foundry  floor,  then  finished  a-nd  faced  with 
finer  material.  They  are  generally  reinforced  by  binders  and 
j aggers  and  are  dried  thoroughly  before  use. 

Cores  are  used  when  holes  are  desired  in  a  casting,  and  are 
usually  made  of  sand  with  some  form  of  extra  "  binder,"  such  as   Feb.&,i905, 
molasses,  flour,  resin,  beer,  gluten  or  some  of  the  many  "  core 
compounds1'  on  the  market.    They  are  shaped  and  baked  before 
putting  in  place. 

Gateing. — The  proper  gateing  of  a  mould  is  quite  as  im- 
portant to  good  castings  as  the  character  of  the  sand.  The  inlets 
should  be  ample  to  admit  the  metal  rapidly  and  should  be  sym- 
metrically placed.  If  more  than  one  is  necessary,  they  should  be 
so  distributed  that  the  metal  will  fill  evenly  and  freely  to  prevent 
cold-shuts.  For  large  castings,  the  gate  should  be  provided  with 
a  •'  riser  "  which  will  hold  reserve  of  molten  metal  to  feed  the  con- 
traction space  of  the  casting. 

Cooling. — As  soon  as  the  metal  has  solidified,  the  castings 
should  be  removed  from  the  moulds  in  order  that  they  may  cool 
naturally.  The  slow  cooling  in  sand  is  equivalent  to  annealing. 
It  will  give  a  large,  open  grain,  accompanied  by  weakness. 

Cleaning. — Small    castings  may  be  cleaned    from  adhering 
sand  by  rotating  in  a  tumble  barrel.     Large  castings  may  be   SJ^hlS'  is 
cleaned  by  means  of  a  sand  blast.     Pickling  in  acids  is  also  prac-   p-  640- 
tised,  although  it  has  a  tendency  to  weaken  the  metal. 

MALLEABLE  CASTINGS. 

The  production  of  malleableized  castings  consists  essentially 
of  first  producing  a  hard,  brittle  casting  of  white  iron  and  subse- 
quently rendering  it  tough  and  malleable  by  further  treatment. 
This  result  may  be  attained  in  two  ways,  either  by  heating  in  the 
presence  of  oxidizing  agents,  such  as  iron  ore,  thereby  removing 
the  carbon  wholly  or  in  part,  or  by  heating  without  oxidizing, 
thereby  converting  the  combined  carbon  largely  into  uncombined, 


322 


Blast  Furnace. 


Jour. 


Franklin 

Inst., 

1899,  II, 

p.  134. 


Am.  Soc. 
Test  Mat., 
Ill,  p.  204. 


when  it  exerts  but  little  influence  upon  the  metal.  This  process 
was  first  described  by  Reaumur  in  1722,  but  was  not  introduced 
into  this  country  until  a  century  later.  The  first  works  in  America 
was  established  at  Newark,  X.  J.,  in  1826.  The  use  of  malleable- 
ized  castings  has  found  wide  application  and  there  are  many  plants 
now  devoted  to  the  industry. 

Melting. — The  metal  for  malleableized  castings  may  be  made 
either  in  the  cupola,  the  open  hearth  or  the  air  furnace,  so  long 
as  the  molten  metal  is  of  the  right  composition.  The  most,  gen- 
erally used  form  of  furnace,  however,  is  the  air  furnace.  It  con- 
sists of  a  rectangular  chamber  with  a  fireplace  at  one  end,  and  the 
chimney  flue  at  the  other.  In  general,  it  differs  but  uttle  from  a 
puddling  furnace,  except  in  the  character  of  its  bottom,  which  is 
made  of  bricks  writh  a  sand  covering.  A  charge  of  pig  is  melted 
down  and  rabbled,  and  the  slag  skimmed  off.  The  oxidizing  action 
during  melting  and  rabbling  permits  the  oxidation  of  the  silicon 
and  some  of  the  carbon.  The  rabbling  and  skimming  is  repeated 
at  intervals  until  a  test  shows  that  the  metal  is  completely  white. 
A  test  is  taken  for  temperature  and  fluidity,  then  the  metal  is 
tapped  into  ladles  and  poured  into  green  sand  moulds,  just  as  in 
the  case  of  gray  iron  castings.  Care  should  be  taken  not  to  chill 
the  surfaces,  as  a  chill  remains  wrhite  during  annealing,  and  af- 
fects the  strength  of  the  casting. 

Annealing. — The  castings  are  freed  from  sand  by  tumbling, 
or  by  pickling  in  dilute  sulphuric  acid,  and  are  then  ready  for  an- 
nealing. They  are  packed  in  fine  ore,  or  roll  scale  in  cast  iron 
boxes  whose  joints  are  luted  with  clay  to  exclude  air.  The  an- 
nealing takes  place  in  ovens  which  must  be  heated  above  redness. 
The  time  necessary  decreases  with  increased  temperature,  the 
minimum  being  60  hours  for  light  castings  and  72  for  heavy.  The 
average  temperature  is  from  1600-1700  degrees  F. 

Rationale. — During  the  period  of  annealing  CO  is  given 
off  at  the  joints  of  the  boxes.  It  burns  with  a  blue  flame  and  the 
iron  content  of  the  ore  rises.  This  shows  that  a  reaction  takes 
place  between  the  oxygen  of  the  ore  or  scale  and  the  carbon  of 
the  metal,  whereby  CO  is  given  off.  The  reason  for  this  action 
becomes  evident  when  we  recall  the  constitution  of  the  metal. 
Carbon  in  iron  may  assume  four  different  forms.  When  the 


Uses  -of  Pig  Iron.  323 

metal  is  high  in  silicon  a  small  portion  of  it  unites  with  the  iron, 
but  the  greater  part  exists  as  graphite.  When  silicon  is  wholly 
or  nearly  absent  the  carbon  exists  in  the  "  combined  "  condition, 
of  which  part  exists  as  a  definite  carbide  or  cementite,  having  the 
formula,  Fe3C,  and  the  remainder  unites  with  the  excess  of  iron 
in  what  is  known  as  the  hardening  condition  or  martensite.  Under 
the  influence  of  heat,  this  combined  carbon  separates  and  forms 
black  spots,  scattered  throughout  the  metal.  These  were  named 
temper  carbon  by  Ledebur.  Temper  carbon  is  black,  solid  car- 
bon, similar  to  graphite  in  nature,  but  differing  from  it  in  the 
fact  that  it  is  amorphous  and  will  recombine  with  iron  at  tem- 
peratures as  low  as  1700  degrees  F.  It  does  not  separate  at  any 
temperature  if  the  total  carbon  is  less  than  0.9  per  cent.  This 
separated  carbon,  which  exists  near  the  surface  of  castings  is 
free  to  unite  with  the  oxygen  of  the  ore  or  scales  which  surround 
it,  and  CO  is  the  result.  Carbon  from  the  interior  of  the  casting 
diffuses  toward  the  surface,  where  it  is  oxidized  in  turn.  In  this 
way  the  quantity  of  carbon  may  be  gradually  decreased,  as  shown 
by  the  following  table. 

Per  cent.  Per  cent.  Per  cent.  Per  cent. 

Time.                                           total  carbon,  hardening  C.  cementite.  temper  C. 

Before  heating 3.338  0.741                  2.507                    

Fourth  day 3.061  0.815                  2.246                   Inst.  Jour 

Fifth  day 2.932  0.859                  2.073                    II,  1897, 

Sixth  day 2.888  0.835                  1.874  0.179    p'  46°' 

Seventh  day 2.098  0.631                  0.430  1.037 

Eighth   day 1.570  0.245                   0.492  0.833 

Ninth  day 1.099  0.656  0.433 

The  percentage  of  carbon  varies  with  the  depth  of  sample.  On 
the  surface  there  is  very  little,  and  the  bulk  is  found  toward  the 
centre  of  the  casting,  as  shown  by  the  following  analyses : 

Place  of  sample.  Combined  C.  Temper  C. 

Outside  layer Tr.  0.00 

Second  layer 0.51  0.00    Ibm., 

Third  layer 0.90  0.38 

Centre  of  casting 1.40  2.38 

Average  of  whole 0.74  1.56 

The  microscope  shows  the  outer  layer  to  consist  of  crystals 
of  ferrite,  surrounded  by  filaments  of  silica  and  oxidized  iron. 
The  second  layer  shows  ferrite  and  pearlite.  The  third  con- 
sists of  pearlite  and  cementite,  while  the  centre  contains  ce- 
mentite and  separated  carbon, 


324  Blast  Furnace. 

Specifications. — The  standard  specifications  for  mallea- 
bleized  castings,  as  proposed  by  the  American  Society  for  Testing 
Materials,  is  as  follows : 

Sulphur  not  over  0.06  per  cent. 

Phosphorus  not  over  0.225  per  cent. 

Tensile  strength  not  under  42,000  pounds  per  square  inch. 

Transverse  strength  not  under  3,000  pounds  per  square  inch  on  a  12-inch  bar. 

Elongation  2K>  per  cent,  in  2  inches. 

Deflection  not  less  than  y2  inch. 

Such  castings  have  more  resilience  than  steel,  and  also  resist 
shock  as  well,  but  have  less  tensile  strength.     It  is  said  that  the 
;    open  hearth  gives  2000  pounds  more  tensile  strength  than  the  air 
'    furnace,  but  the  air  furnace  can  make  metal  of  52,000  tensile 
strength.      The   usual   limits   of   tensile    strength   are   40,000   to 
63,000. 

Action  of  Metalloids  During  Annealing — The  presence  of 
sulphur  delays  annealing,  since  it  tends  to  keep  the  carbon  in  the 
combined  state  and  consequently  opposes  its  elimination.  It 
should,  therefore,  not  greatly  exceed  0.05  per  cent.  There  is  a 
tendency  also  to  take  up  sulphur  during  annealing.  Phosphorus 
tends  to  make  the  metal  hard  but  fluid.  Its  limit  is  usually  set  at 
0.2  per  cent.  Manganese  is  a  hardener  also,  but  it  tends  td  elimin- 
ate sulphur  during  melting  and  so  may  become  beneficial.  It 
should  never  exceed  1.5  per  cent. 

Silicon  should  be  kept  low,  in  order  that  the  castings  may  be 
perfectly  white  before  annealing,  but  it  should  not  be  entirely 
absent,  as  some  seems  to  be  necessary  in  order  to  facilitate  the 
separation  of  the  temper  carbon.  The  silicon  which  is  required  to 
release  the  carbon  is  about  as  follows : 

Heavy  castings 0.45  per  cent.  Si. 

Eng'xLrx'  Ordinary  castings 0.65  per  cent.  Si. 

p.  53!.'  Agricultural   castings 0.80  per  cent.  Si. 

Very   light   castings 1.25  per  cent.  Si. 

A  composition  which  would  show  perfectly  white  fracture  in 
small  sections  might  show  graphite  in  a  large  section  which  cools 
more  slowly.  Usually  about  35  per  cent  of  the  silicon  in  the  pig 
is  lost  during  melting,  so  the  pig  should  contain  0.75  to  1.50  per 
cent.,  according  to  the  class  of  work.  Generally  an  additional 
20  to  40  per  cent,  is  lost  during  annealing. 

Under  ordinary  conditions  there  is  no  considerable  elimination 


Uses  of  Pig  Iron.  325 

of  carbon  during  melting  Any  drop  in  percentage  is  due  chiefly 
to  the  additions  of  less  carburized  metal  in  the  form  of  steel, 
scrap  and  rabbles.  Any  attempt  to  eliminate  the  carbon  in  the 
furnace  will  result  in  excessive  oxidation  of  the  metal.  The  drop 
in  carbon  usually  ranges  from  0.2  to  0.4  per  cent.  The  lower 
the  carbon,  the  less  annealing  is  necessary,  but  a  good  percentage 
is  required  to  give  fluidity  and  clear  castings.  The  iron  used  may 
contain  the  usual  content  of  carbon,  i.  e.,  from  2.75  to  4.00  per 
cent.  The  carbon  must  be  wholly  in  the  combined  state  in  the 
castings,  as  graphite  is  not  affected  by  annealing  and  its  presence 
interferes  with  both  strength  arid  malleability. 

Shrinkage. — The  contraction  of  white  iron  is  high,  and  the 
castings  usually  show  a  shrinkage  of  very  near  )4  inch  per  foot, 
which  is  about  double  that  of  gray  iron.  During-  annealing-  how- 

,         ...   *  Iron  Trade 

ever,  the  separation  ot  solid  carbon  causes  an  expansion  which    Review, 

r  1900,  Apr.  5. 

more  than  compensates  for  the  excess  of  contraction.  As  a  re- 
sult the  net  shrinkage  of  malleable  castings  averages  somewhat 
less  than  that  of  gray  castings. 

Effects  of  Heat  Alone. — Cold  white  iron  may  be  considered 
as  consisting  of  a  mass  of  cementite  and  pearlite.  When  it  is 
heated  to  about  1300  degrees  F.,  which  is  a  critical  point,  known 
as  the  "  recalescence  point,"  the  pearlite  becomes  a  homogeneous 
carbide,  approximating  the  formula,  Fe24C,  which  contains  0.85 
per  cent.  C.  As  the  temperature  rises  above  1800  degrees  F.,  the 
Fe3C  is  decomposed  and  unites  with  the  Fe24C  to  form  a  combina- 
tion having  a  different  degree  of  concentration  corresponding  to 
the  formula  Fe14C,  and  containing  1.5  per  cent.  C.  Any  excess 
of  carbon  will  then  separate  as  temper  carbon,  and  give  the  iron 
a  gray  or  black  appearance  sometimes  known  as  "  black  heart  " 
castings.  This  principle  serves  as  the  basis  for  the  manufacture 
of  "  converted  gray  castings." 

Converted  Gray  Castings — Converted  gray  castings  stand 
between  gray  iron  castings  and  malleableized  castings  in  that  white 
castings  are  rendered  somewhat  malleable  through  annealing,  but 
without  any  removal  of  carbon.  Gray  castings  are  made  by  heat- 
ing white  castings  under  a  protecting  cover  to  prevent  scaling,  to 
1850  degrees  F.  for  a  few  hours.  The  white  surface  of  the  metal 
becomes  uniformly  gray  throughout,  and  the  structure  becomes 


326 


Blast  Furnace. 


v  News,    Before   annealing 


' 


Jour 


Frank. 

i8oo"iV 
p-  22  • 


.  A  s.  c,  E. 
NO.  34,  p. 


After  annealing 


C.  C.    Temper  C.     Si.  Mn. 

2.00          0.72          0.71          0.110 
0.82          2.75          0.73          0.108 


more  dense.  The  metal  is  not  so  malleable  as  malleableized  cast- 
ings, but  it  can  be  forged  and  has  a  tensile  strength  of  over 
40,000  pounds.  The  change  which  takes  place  is  illustrated  by 
the  following  analysis: 

P.  S. 

0.039          0.045 
0.039          0.040 

The  presence  of  silicon  assists  in  the  conversion.  The  higher 
^ie  smcon  tne  less  neat  and  time  are  necessary  for  the  change 
and  the  more  thoroughly  is  it  accomplished.  When  Si  is  below 
y2  per  cent.,  the  change  becomes  very  difficult.  The  limit  of 
silicon  is  indicated  by  the  appearance  of  graphite  in  the  casting. 

Effects  of  Various  Methods.  —  The  following  table  illus- 
trates the  effect  upon  white  iron  of  various  conditions  of  anneal- 
ing: 


Cover. 
White  iron 

C.  C. 
3  69 

Temper  C. 
0.19 
2.80 
2.73 
2.30 
1.79 
1.75 
1.60 
0.36 
0.49 
0 

Angle 
Tensile                                               of  bend, 
strength.  Elongation.  Reduction,  deg.  F. 
15,600              000 
28,000              000 
28,200              000 
44.400              0                    0                    10 
38,600              1.90              3.15               75 
36,800              2.10              2.10              75 
40,200              2.20              3.05              75 
32,600              4.60              2.10              80 
30,800              5.60              3.10              90 
33,20              10.80              7.96            180 

Cbarcoal*     

.  .0.94 
..0.99 
..0.81 
.  .0  64 

Cast  borings*  
Wrought  drillings*.. 
Limef                     .  .  .  . 

Sandf 

.    0  63 

0  68 

Hematite      . 

.  .0.73 

.  .  0.58 

Orp    three  times.  . 

.  .Tr. 

*  Luted. 


t  With  access  of  air. 


Decarburization  appears  to  be  most  rapid  and  most  complete  in 
an  atmosphere  of  CO2. 

Charcoal  pig  in  some  proportion  was  long  considered  indis- 
pensable  to  the  production  of  malleable  castings,  but  an  average 
Q£  ^  tests  eac]1?  Of  coke  anc{  charcoal  irons  show  that  coke  iron 
gives  castings  which  give  higher  tensile  strength  as  well  as  better 
elongation  and  reduction. 


APPENDIX   I. 

SOME    PRINCIPLES    OF   CHEMISTRY   AND    PHYSICS, 
CHANGES  IN  MATTER. 

Matter  is  a  general  term  used  by  scientists  to  include  all  mate- 
rial substance  which  exists  in  the  universe.  It  occurs  in  infinite 
varieties  of  form  and  nature,  and  the  study  of  it  forms  the  basis 
of  such  natural  sciences  as  Chemistry  and  Physics.  The  quantity 
of  matter  in  the  universe  is  constant.  It  does  not  lie  within  the 
power  of  the  scientist  to  either  create  or  destroy  matter.  His 
power  is  limited  to  merely  changing  its  form  or  condition,  and  it 
is  through  this  power  that  all  matUncan  be  adapted  to  his  pur- 
pose. Changes  in  matter  may  be  classed  under  two  general 
heads.  When  the  change  is  superficial  and  does  not  alter  the 
essential  composition  of  the  substance,  it  is  denoted  as  physical 
when  it  is  so  fundamental  as  to  alter  the  composition  of  the  sub- 
stance it  is  known  as  chemical.  This  distinction,  when  once  un- 
derstood is  usually  quite  obvious,  but  in  certain  phases  of  the 
study  it  is  difficult  to  tell  where  one  ends  and  the  other  begins. 

CHEMICAL  CHANGES  IN  MATTER. 

The  science  of  Chemistry  deals  with  the  composition  of  mat- 
ter. Any  change  in  the  composition  of  matter  is  known  as  chem- 
ical change,  which  must  be  carefully  distinguished  from  mere 
physical  change.  Change  in  position,  shape  or  temperature,  etc., 
does  not  alter  the  nature  of  the  substance  and  is  therefore  simply 
physical.  For  example,  the  cutting  of  timber,  the  forging  of 
steel  and  the  melting  of  lead  leave  each  kind  of  material  un- 
changed in  its  essential  nature.  There  has  been  no  change  in  the 
constitution  of  the  substances  involved.  If,  on  the  other  hand, 
the  wood  be  burned  to  invisible  gases,  or  the  metal  be  oxidized  to 
brittle  scale,  there  has  been  essential  change  in  the  nature  of  the 
substances.  The  old  substances  have  passed  into  new  combina- 
tions with  other  associations  and  properties,  and  there  has  been 
chemical  change.  Every  chemical  change  is  accompanied  by  radi- 
cal change  in  the  nature  of  the  substance. 

327 


328  Blast  Furnace. 

NATURE  OF  MAPTER. 

All  matter,  however  complex,  must  be  made  up  of  elementary 
substances.  By  separation  or  analysis  a  chemist  may  discover 
what  elementary  substances  combine  to  form  a  given  mass  of 
matter.  He  can  go  a  step  farther  and  prove  the  accuracy  of  his 
observations  by  synttfesis,  that  is  by  causing  similar  elementary 
substances  to  combine,  thereby  reproducing  the  original  kind  of 
matter. 

ELEMENTARY   SUBSTANCES. 

In  separating  the  component  parts  of  matter  the  chemist  finds 
that  certain  components  appear  incapable  of  further  separation. 
For  example,  oxides  of  iron  can  be  easily  separated  into  Fe  and 
O,  but  neither  can  be  made  to  undergo  further  division.  These 
indivisible  components  are  assumed  by  scientists  to  be  reduced  to 
their  lowest  terms,  and  are  therefore  called  elements.  It  is 
not  beyond  the  bounds  of  possibility  that  some  or  all  of  what  are 
now  considered  elements  may  some  time  be  broken  up  still  further, 
but  so  far  they  have  resisted  all  the  skill  of  science,  and  so  may 
be  considered  by  us  in  all  respects  as  strictly  elementary  bodies. 

Atoms — While  an  element  cannot  be  separated  into  compo- 
nent elements,  it  may  be  capable  of  very  fine  subdivision.  A  bar 
of  iron,  for  instance,  may  be  reduced  to  iron  filings,  and  each 
grain  of  filings  may  be  divided  still  further.  This  subdivision 
may  be  conceived  as  continued  until  the  most  minute  particle 
which  can  exist  is  reached.  This  ultimate  particle  of  an  element 
is  called  an  atom.  Atoms  of  all  kinds  seem  to  be  made  up  of  still 
more  minute  particles  called  corpuscles,  but  for  the  present  dis- 
cussion an  atom  may  be  considered  the  final  product  of  subdi- 
vision. 

Atomic  Weights — Such  a  tiny  particle  of  matter  as  a  chem- 
ical atom  could  hardly  be  considered  as  having  much  size  and 
weight,  yet  it  must  necessarily  have  both.  It  is  impossible,  of 
course,  for  us  actually  to  weigh  in  pounds  and  ounces  such  im- 
ponderable masses,  and  yet  we  have  a  list  of  the  atomic  weights 
of  the  elements.  These  weights  are  not  absolute,  but  relative, 
and  represent  the  comparative  weights  of  the  simplest  combining 
proportion  of  each  element.  Scientists  have  concluded  that  the 


Some  Principles  of  Chemistry  mid  Physics.  329 

smallest  weight  in  which  a  given  element  has  ever  been  found  in 
combination  must  be  the  weight  of  its  smallest  subdivision;  that 
is,  its  atom.  In  default  of  a  scale  of  weights  sufficiently  delicate 
for  such  comparisons  it  was  necessary  to  improvise  one,  the  basis 
of  which  is  the  lightest  known  atom.  Hydrogen  is  the  element 
that  has  the  distinction  of  being  found  in  combination  with  other 
elements  in  the  smallest  proportion  by  weight,  hence  the  weight 
of  its  atom  is  taken  as  the  standard  and  designated  as  i.  The 
combining  weights  of  all  the  other  elements  have  been  determined 
very  carefully  on  this  basis. 

The  combining  weights  of  the  elements  must  not  be  confused 
with  absolute  weight,  or  weight  per  cubic  foot.  The  latter  is 
known  as  the  specific  gravity  of  the  substance,  and  is  usually  ex- 
pressed as  the  ratio  of  the  weight  of  a  unit  volume  of  the  sub- 
stance to  the  weight  of  the  same  volume  of  water.  For  example, 
a  cubic  foot  of  water  weighs  62.4  pounds  and  a  cubic  foot  of  cast 
iron  weighs  450  pounds.  The  specific  gravity  of  cast  iron,  there- 

45° 

fore,  is  -^ — =  7.2. 
62.4 

Chemical  Notation. — By  common  consent  the  notation  of 
chemical  elements  has  been  abbreviated  to  symbols  which  are 
usually  the  initial  letters  of  the  English  or  Latin  name.  The  use 
of  the  symbol  alone  signifies  that  only  one  atom  of  the  element 
is  involved.  Two  or  more  atoms  are  indicated  by  a  small  sub- 
script figure  written  after  the  symbol.  For  example,  O  stands 
for  oxygen  and  Fe  stands  for  iron,  (Latin,  ferrum).  Fe2O3 
stands  for  a  compound  of  two  atoms  of  iron  and  three  of  oxygen. 
The  atoms  of  elementary  substances  appear  to  unite  with  each 
other,  usually  in  pairs,  to  form  molecules  of  great  stability,  as 
O2,  N2,  etc. 

Nature  of  Elements — The  elements  with  which  most  of 
us  are  best  acquainted  are  probably  the  metals.  Most  of  the 
metals  which  we  use  daily  are  elements,  except  a  few,  such  as 
bronze,  brass,  babbitt,  solder,  etc.,  which  are  alloys  of  two  or 
more  metals.  Elements  are  not  all  metals,  however,  nor  are  they 
even  solids  at  ordinary  temperatures.  Some  exist  as  liquids  and 
several  as  gases. 

Mixture    of    Elements.—Elements  may  usually  be  mixed  to- 


330  Blast  Furnace. 

gether  under  ordinary  conditions  without  undergoing  change.  A 
conspicuous  example  of  this  is  atmospheric  air  which  we  breathe. 
Air  is  a  mixture  of  the  two  gases,  oxygen  and  nitrogen,  in  the 
proportion  of  20.9  parts  to  79.1  parts  respectively  by  volume,  and 
23.3  parts  to  76.7  parts  by  weight.  There  are  traces  of  other 
gases  in  the  air,  but  the  total  is  small  in  comparison  to  the  quanti- 
ties of  O  and  N.  Although  air  is  simply  a  mixture  of  O  and  X, 
these  proportions  hold  good  the  world  over.  The  components  of 
air  may  be  separated  and  examined.  They  are  found  to  be  per- 
fect gases  under  all  ordinary  conditions  of  temperature  and  pres- 
sure and  respond  to  all  of  the  laws  to  which  gases  are  subject. 
Air,  likewise,  is  a  perfect  gas,  and  is  governed  by  all  the  laws  of 
gases.  Hence  we  see  that  these  two  gases,  when  put  together, 
form  another  perfect  gas,  which,  since  it  partakes  of  the  proper- 
ties of  each  must  be  simply  a  mixture. 

COMPOUNDS. 

Chemical  elements  enter  into  definite  combination  with  each 
other  in  proportion  to  their  atomic  weights.  These  combinations 
are  known  as  compounds.  In  forming  a  compound  the  combin- 
ing elements  involved  lose  their  identity  completely,  and  form  a 
new  substance  that  may  differ  widely  from  them.  For  instance, 
two  gases  may  unite  to  form  a  liquid,  or  a  gas  and  a  liquid  may 
unite  to  form  a  solid.  It  is  such  radical  changes  in  characteristics 
that  enable  us  to  determine  whether  a  given  change  is  chemical 
or  merely  physical. 

Molecules — The  smallest  particle  of  a  compound  which  can 
exist,  that  is,  one  which  cannot  be  further  subdivided  without 
separating  it  into  its  component  atoms,  is  called  a  molecule. 
The  molecule  bears  the  same  relation  to  the  compound  that  the 
atom  does  to  the  element,  in  that  it  is  the  smallest  conceivable 
portion  of  it.  Each  molecule  of  a  given  compound,  however,  is 
composed  of  the  same  number  of  the  same  kind  of  atoms  as  every 
other  molecule. 

Quantivalence — Atoms  have  the  property  of  uniting  with 
other  atoms  according  to  a  certain  numerical  law,  which  is  desig- 
nated as  quant i valence.  For  example,  the  hydrogen  atom  appears 
to  possess  but  a  single  bond  for  uniting  with  other  elements,  hence 


Some  Principles  of  Chemistry  and  Physics.  331 

it  is  denominated  a  univalent  element.  Oxygen  possesses  two 
bonds  and  is  said  to  be  bivalent,  nitrogen  three,  and  is  trivalent, 
silicon  four  and  is  quadrivalent,  phosphorus  five  and  is  quinquiva- 
lent, chromium  six  and  is  hexivalent.  Under  certain  conditions 
two  adjacent  bonds  in  a  given  atom  may  unite  with  each  other 
and,  in  consequence,  a  hexivalent  atom  may  appear  temporarily 
to  be  quadrivalent  or  bivalent,  and  a  quinquivalent  element  may 
appear  trivalent  or  univalent.  Such  an  element  may  be  described 
as  unsatisfied  or  unsaturated,  and,  in  consequence,  usually  forms 
additional  relations  readily. 

Composition  of  Water — One  of  the  simplest  compounds, 
and  one  that  is  very  familiar  to  all,  is  water.  Like  air,  it  is  com- 
posed of  two  gases,  but,  unlike  air,  the  gases  are  combined  and 
not  merely  mixed.  The  components  of  water  are  hydrogen  and 
oxygen.  Since  the  hydrogen  atom  possesses  only  one  bond  and 
the  oxygen  atom  has  two,  the  law  of  quantivalence  makes  it  nec- 
essary that  the  water  molecule  shall  consist  of  two  atoms  of  hydro- 
gen and  one  of  oxygen,  or  some  simple  multiple.  It  is  generally 
considered  that  the  simplest  formula  is  the  true  one,  hence  it  is 
written  H2O,  in  accordance  with  the  chemical  notation,  which 
shows  at  a  glance  the  chemical  composition  of  substances. 

Classification  of  Compounds — H2O  may  be  considered  as 
a  type  of  compounds  in  general.  The  hydrogen  may  be  replaced 
by  any  of  the  simple  elements  except  Fluorine,  and  by  many  com- 
binations made  up  of  two  or  more  elements.  Such  a  group  re- 
placing hydrogen  in  any  of  its  compounds  is  known  as  a  basic 
radical.  On  the  other  hand,  the  oxygen  of  H2O  may  be  replaced 
by  various  elements  or  groups  of  elements,  and  such  replacing 
groups  are  known  as  acid  radicals.  Acid  radicals,  replacing  the 
oxygen  of  water,  give  a  class  of  compounds  known  as  acids. 
When  acid  and  basic  radicals  unite,  the  combinations  are  known 
as  salts.  The  replacement  of  the  hydrogen  of  water  by  other  ele- 
ments brings  into  existence  a  class  of  compounds  known  as 
oxides.  When  the  replacing  elements  are  simple  metals,  the 
metallic  oxides  so  formed  are  known  as  bases, 

OXIDATION  AND  REDUCTION. 

The  process  of  attaching  oxygen  to  an  element  is  known  as 
oxidation,  and  the  element  is  said  to  be  oxidized.  The  removal  of 


332  Blast  Furnace. 

oxygen  from  an  oxidized  compound  is  called  reduction,  and  the 
operation  is  described  as  "  complete  "  or  "  partial,"  according  to 
whether  the  oxygen  is  wholly  or  only  partially  removed.  The 
oxidation  of  a  substance  is  a  chemical  operation  and  the  product 
of  the  action  is  always  very  different  from  the  initial  components. 
For  example,  the  oxidation  of  iron  produces  rust  or  scale,  which 
presents  no  resemblance  to  either  a  strong,  tough  metal  or  a  gas. 
The  combustion  of  wood  or  coal  is  nothing  else  than  the  phe- 
nomenon produced  by  the  uniting  of  the  oxygen  of  the  air  with 
the  carbon  and  hydrogen  of  the  fuel. 

Oxidizing  Agents. — Oxygen  is  a  particularly  aggressive 
element,  and  as  it  is  present  everywhere  in  the  atmosphere,  oxida- 
tion of  other  elements  frequently  takes  place  spontaneously.  The 
rusting  of  iron  is  the  result  of  slow,  spontaneous  union  going  on 
between  the  metal  and  the  atmospheric  oxygen.  Any  protective 
coating  that  keeps  iron  from  contact  with  the  oxygen  of  the  air 
will  prevent  rusting.  Oxidation  of  substances  in  contact  with 
air  would  be  much  more  rapid  if  the  aggressiveness  of  oxygen 
were  not  restrained  by  the  presence  of  nitrogen.  Nitrogen  is  as 
inert  as  oxygen  is  active,  and,  as  it  comprises  four  fifths  of  the 
atmosphere,  it  dilutes  its  aggressive  companion  to  such  an  extent 
that  its  activity  is  enormously  reduced.  For  example,  we  know 
that  oxidation  of  iron  by  the  atmosphere,  in  the  familiar  form  of 
rusting  is  a  comparatively  slow  process.  If,  however,  there  be 
prepared  a  jar  of  pure  oxygen,  free  from  the  restraining  influ- 
ence of  nitrogen,  and  a  piece  of  iron  wire,  heated  to  redness  at 
one  end,  be  thrust  into  it,  the  wire  will  burn  as  actively  as  does  a 
splinter  of  wood  in  ordinary  air.  It  will  give  off  a  bright,  spark- 
ling light,  and  in  a  few  seconds  be  changed  to  bits  of  black  scale, 
closely  resembling  the  scale  from -a  rolling  mill. 

We  have  seen  that  oxidation  of  elements  may  take  place 
under  certain  conditions  through  direct  contact  with  oxygen  gas. 
It  may  also  take  place  by  a  method  of  exchange  between  oxidized 
and  unoxidized  substances.  A  necessary  condition  to  the  reaction, 
however,  is  that  under  the  existing  circumstances  the  unoxidized 
substance  must  have  a  stronger  attraction  for  the  oxygen  than 
does  the  oxidized  substance.  For  example,  at  certain  moderately 
high  temperatures,  carbon  dioxide,  CO2,  will  give  up  part  of  its 


Some  Principles  of  Chemistry  and  Physics.  333 

oxygen  to  metallic  iron.  The  exchange  may  be  represented  graph- 
ically by  this  equation, 

CO,  +  Fe  =  CO  +  FeO, 

in  which  we  see  that  one  of  the  atoms  of  oxygen  has  left  the  CO2, 
and  attached  itself  to  the  Fe,  thereby  partially  oxidizing  the  iron 
to  FeO,  and  partially  reducing  the  carbon  to  the  condition  of  CO. 
As  a  matter  of  fact,  this  reaction  is  not  so  simple  in  reality  as  the 
above  equation  would  indicate.  In  this  simplified  form  it  serves 
only  as  an  illustration  of  the  general  principle  involved.  It  should 
be  observed  that  in  this  case  of  oxidation  of  iron  by  transfer  of 
oxygen,  there  is  of  necessity  a  corresponding  reduction  of  the 
carbon.  In  the  case  of  oxidation  by  direct  contact  with  oxygen 
gas  there  was  no  accompanying  reduction,  because  the  oxygen 
used  was  already  free.  In  oxidation  by  means  of  oxidized  sub- 
stances, it  is  evident  that  reduction  must  precede  oxidation  in  or- 
der that  the  necessary  oxygen  may  be  available  for  the  purpose. 
Since  both  reactions  take  place,  it  is  customary  to  designate  the 
operation  according  to  the  reaction  that  we  are  endeavoring  to 
accomplish. 

HEAT  OF  COMBUSTION. 

In  the  process  of  combining  elements  to  form  chemical  com- 
pounds, heat  is  given  off  by  some  reactions  and  absorbed  by  oth- 
ers. The  quantity  of  heat  has  been  measured  many  times, 
and  it  is  found  that  a  given  quantity  of  material  entering  into  a 
given  reaction  always  involves  the  same  quantity  of  heat.  Those 
reactions  that  give  off  heat  are  called  exothermic  reactions, 
and  those  that  absorb  heat  are  called  endothermic  reactions.  The 
union  of  oxygen  with  the  other  elements  with  which  we  have  to 
deal  is  always  exothermic.  It  is  this  property  of  oxidation  that 
makes  fuels  efficient  heat  producers.  Fuels,  such  as  wood,  coal, 
petroleum,  etc.,  are  made  up  of  carbon  and  hydrogen.  The  proc- 
ess of  combustion  is  merely  the  rapid  oxidation  of  these  two  ele- 
ments by  the  oxygen  of  the  atmosphere.  Such  oxidation  does 
not  take  place  at  ordinary  temperatures.  There  is  a  definite  tem- 
perature for  each  combustible  substance  known  as  the  "  ignition 
point,"  at  which  rapid  oxidation  begins.  The  combustion  then 
continues  as  long  as  the  temperature  of  the  flame  keeps  above  the 


334  Blast  Furnace. 

ignition  point  of  that  substance.  Spontaneous  combustion  occurs 
when  internal  heating  raises  the  temperature  of  a  combustible  to 
the  ignition  point.  Decay  of  organic  substance  is  a  slow  oxidation 
at  ordinary  temperatures.  The  amount  of  heat  given  out,  how- 
ever, is  the  same  as  if  the  substance  had  been  burned  by  rapid 
oxidation. 

COMBINATIONS   OF  OXIDES. 

As  was  observed  above,  the  oxides  of  metals  are  usually 
termed  bases.  The  chief  bases  with  which  we  will  deal  are  the 
oxides  of  iron,  manganese,  calcium,  magnesium,  sodium  and 
potassium.  The  non-metallic  elements  are  usually  acid-makers, 
such  as  silicon,  sulphur,  phosphorus,  carbon  and  nitrogen.  These 
acid  and  basic  radicals  when  in  solution  react  upon  each  other 
and  produce  a  class  of  compounds  called  salts.  For  example, 
CaO  may  be  considered  as  uniting  with  SO3  to  form  the  salt,  cal- 
cium sulphate,  CaSO4.  In  the  same  way,  we  may  consider  that 
MgO  and  CO2  unite  to  form  magnesic  carbonate,  MgCCX,  or 
Na2O  and  SiO2  to  form  sodic  silicate,  Na2SiO3.  When  these 
oxides  are  brought  into  contact  in  a  state  of  fusion,  they  show  the 
same  affinities  as  when  in  solution,  although  the  outward  effect  is 
vastly  different.  The  slags  from  metallurgical  operations  are  the 
result  of  such  fusion. 

Slag  is  a  general  term  which  covers  a  various  and  complex 
class  of  bodies.  The  name  is  applied  to  the  scoria  which  is  present 
in  all  metallic  fusions  and  which  may  vary  in  composition  from 
fused  metallic  oxides,  carrying  little  or  no  acid  constituents,  to 
highly  siliceous  compounds  having  but  a  small  percentage  of 
bases.  The  slag  from  an  iron  blast  furnace  is  usually  composed 
largely  of  calcium  silicate,  although  the  calcium  may  be  partially 
replaced  by  magnesium  and  the  silica  by  aluminum. 

REDUCING  AGENTS. 

We  have  seen  that  oxidation  may  take  place  with  or  without 
a  corresponding  reduction.  On  the  other  hand,  reduction  is  al- 
ways accompanied  by  a  corresponding  oxidation.  The  reduction 
of  iron  oxide,  for  example,  may  be  accomplished  by  means  of 
several  reducing  agents,  but  in  each  case,  the  latter  undergoes 
corresponding-  oxidation,  thus. 


Sonic  Principles  of  Chemistry  and  Physics.  335 

Fe203  +  3H2  =  Fe2  +  3H2O. 

Fe203  +  3C  =  Fe2  +  3CO. 

Fe203  +  3CO  =  Fe2  +  3CO2. 

The  occurrence  of  these  interchanges  demands  as  a  rule,  cer- 
tain specific  conditions.  The  ruling  condition  is  usually  the  tem- 
perature, but  it  is  also  of  first  importance  that  the  different  sub- 
stances should  be  brought  into  intimate  contact  for  a  sufficiently 
long  period  for  the  interchange  to  take  place.  Each  of  the  above 
reducing  agents  has  a  critical  temperature  below  which  it  refuses 
to  act.  Hydrogen  will  attack  the  oxide  at  temperatures  lower 
than  C  or  CO.  It  is  active  at  all  temperatures  above  the  boiling 
point  of  water,  212  degrees  F.  Carbon  monoxide  does  not  begin 
to  reduce  iron  until  about  400  degrees  F.  is  reached,  while  carbon 
needs  a  temperature  of  nearly  800  degrees  F.  At  temperatures 
above  redness,  the  action  of  CO  may  be  reversed  and  the  re- 
duced iron  will  be  oxidized  by  the  CO2  formed  by  the  reaction. 
As  a  matter  of  fact,  most  chemical  reactions  are  reversible  under 
other  conditions  of  temperature  and  pressure.  The  point  of 
equilibrium  under  a  given  set  of  conditions  depends  upon  the 
relative  concentrations  of  the  agents  present,  the  nature  of  the 
reaction  being  determined  by  the  agent  having  the  greatest  con- 
centration. This  fact  is  the  basis  for  the  Law  of  Mass  Action. 
Reactions  that  produce  compounds  which  neutralize  the  reagents 
will  check  themselves,  unless  the  neutralizing  compounds  are  con- 
tinually removed  from  the  point  of  action.  It  is  evident,  there- 
fore, that  reactions  cannot  be  complete  unless  they  produce  in- 
soluble or  volatile  compounds. 

DESCRIPTION    OF    CERTAIN    ELEMENTS. 

Only  a  few  of  the  seventy  odd  elements  that  have  been  dis- 
tinguished are  involved  in  the  metallurgy  of  iron.  It  is  inad- 
visable for  a  beginner  in  the  study  to  burden  his  mind  with  other 
elements  than  those  which  are  essential.  A  brief  ^description  of 
the  most  important  facts  concerning  the  few  that  are  necessary 
is  given  below. 

OXYGEN.      O. 

Oxygen  is  a  transparent,  colorless  gas  with  neither  taste  nor 
smell.  In  appearance  it  cannot  be  distinguished  from  ordinary 


Blast  Furnace. 

air.  It  is  the  most  abundant  substance  in  the  universe.  It  com- 
prises eight-ninths  of  all  the  water,  one  half  of  all  the  land  and 
one  fifth  of  all  the  air,  besides  entering  largely  into  the  compo- 
sition of  plants  and  animals.  It  combines  with  all  other  elements 
except  one,  which  indicates  that  it  is  the  most  active  or  most 
popular  of  all  the  elements.  In  the  act  of  combining  with  other 
elements,  it  gives  out  heat  and  frequently  light,  producing  the 
phenomenon  known  as  combustion.  Its  activity  is  such  that  if  the 
oxygen  of  the  air  were  not  diluted  with  four  times  as  much  nitro- 
gen, no  substances  of  an  oxidizable  nature  could  long  withstand 
its  presence,  and  we  would  be  constantly  subjected  to  spontane- 
ous combustion. 

Oxide  Compounds — When  oxygen  enters  into  combination 
with  the  other  elements  singly,  the  resulting  compounds  are 
known  as  oxides.  Many  such  oxides,  when  combined  with  water, 
become  members  of  the  class  of  compounds  known  as  acids.  For 
example, 

SO3  +  H2O  =  H2SO4,  sulphuric  acid. 
CO2  +  H2O  ==  H2CO3,  carbonic  acid. 
SiO,  +  H2O  =  H2SiO3,  silicic  acid. 

In  fact  the  word  oxygen  means  "  acid-maker."  The  above  exam- 
ples show  that  some  acids  at  least  are  but  hydrated  oxides. 
Oxides  that  can  be  obtained  by  dehydrating  an  acid  in  this  way 
are  known  as  anhydrous  oxides  or  anhydrides.  For  example, 
sulphuric  trioxide,  SO3,  is  called  sulphuric  anhydride,  and  car- 
bonic oxide,  CO,,  and  silicic  dioxide,  SiO2,  are  sometimes  called 
carbonic  and  silicic  anhydrides. 

The  great  duty  of  oxygen  in  the  universe  is  to  support  com- 
bustion. Oxygen,  itself,  does  not  burn,  that  is  to  say  it  cannot 
unite  with  itself.  But  it  is  absolutely  necessary  to  the  combustion 
of  other  materials,  since  combustion  is  but  the  oxidation  of  mat- 
ter. 

NITROGEN.      N. 

Like  oxygen,  nitrogen  is  a  transparent,  colorless,  tasteless, 
odorless  gas  not  easily  to  be  distinguished  from  air.  It  is  not 
surprising  that  both  oxygen  and  nitrogen  resemble  air,  since  it 
is  but  a  simple  mixture  of  the  two.  In  its  behavior,  nitrogen  is 
very  unlike  oxygen.  While  oxygen  is  the  most  active  element, 


Sonic  Principles  of  Chemistry  and  PJiysics.  337 

nitrogen  is  very  inert.  It  is  singularly  indifferent  to  forming 
compounds  with  other  elements.  It  docs  form  such  compounds, 
but  only  with  reluctance.  This  is  well  illustrated  during  the 
passage  of  the  blast  of  air  through  the  blast  furnace.  During 
that  time  the  oxygen  of  the  air  is  entirely  consumed,  losing  its 
identity  entirely,  but  the  great  bulk  of  the  nitrogen  passes  out  of 
the  furnace  unchanged.  A  small  portion,  however,  unites  with 
carbon  at  the  high  temperatures  of  the  furnace  and  forms  cyan- 
ogen, CN,  which  is  the  basis  of  all  cyanides. 

Although  when  mixed  with  oxygen  nitrogen  forms  air,  which 
supports  combustion  and  life,  yet  when  alone  it  extinguishes 
flame,  purely  for  lack  of  oxygen.  It  does  not,  therefore,  play  an 
important  part  in  metallurgical  operations,  although  its  universal 
presence  makes  it  necessary  that  it  be  fully  understood  and  al- 
lowed for. 

HYDROGEN.      H. 

Hydrogen,  when  pure,  is  a  transparent,  colorless,  tasteless, 
odorless  gas,  not  easily  to  be  distinguished  in  appearance  from 
oxygen,  nitrogen  or  air.  Like  nitrogen,  it  is  incapable  of  support- 
ing combustion.  The  flame  of  what  are  ordinarily  considered 
combustibles  will  not  live  in  an  atmosphere  of  hydrogen.  In  the 
presence  of  oxygen,  however,  it  is  itself  exceedingly  inflammable, 
that  is  to  say,  it  has  a  very  strong  affinity  for  oxygen.  The  igni- 
tion point,  or  the  point  at  which  the  two  begin  to  combine,  is 
comparatively  low,  and  the  heat  of  the  reaction  is  very  high,  the 
reaction  giving  off  more  heat  than  any  other  known.  Burning 
hydrogen  is  often  used  for  producing  very  high  temperatures. 
The  product  of  such  combustion  is  hydrogen's  most  important 
compound,  water,  in  the  form  of  very  highly  heated  steam,  thus, 

2H2  +  O2  =  2H2O. 

A  mixture  of  hydrogen  with  oxygen  or  air  is  very  explosive.  Its 
affinity  for  oxygen,  however,  is  not  confined  to  oxygen  in  the  free 
state,  but  it  has  a  strong  attraction  for  oxygen  when  combined 
with  other  elements.  It  is  therefore  a  powerful  reducing  agent, 
one  of  the  most  powerful  known.  It  attacks  oxides  of  iron,  and 
reduces  them  to  the  metallic  condition  with  ease  at  comparatively 
row  temperatures  with  the  accompanying  formation  of  water.  It 


338  Blast  Furnace. 

is  the  lightest  substance  known,  and,  as  has  been  stated,  the  weight 
of  its  atom  serves  as  the  standard  from  which  we  compute  the  rel- 
ative weights  of  the  atoms  of  the  other  elements. 

CARBON,     c. 

Carbon  is  a  very  abundant  element  and  one  that  is  extremely 
important  in  metallurgical  operations.  It  is  widely  distributed 
and  appears  under  many  guises.  For  example,  charcoal,  graphite 
or  plumbago,  coke,  lampblack,  soot  and  even  the  diamond,  are  but 
different  modifications  of  this  same  substance.  When  combined 
with  other  elements,  in  the  form  of  certain  hydrocarbon  gases,  it 
forms  also  coal,  wood  and  all  other  organic  substances.  It  is 
even  a  constituent  of  certain  rocks,  such  as  limestone,  dolomite 
and  spathic  iron  ore.  Since  it  is  the  chief  constituent  of  wood, 
coal,  coke,  charcoal  and  most  combustible  gases,  it  is  plainly  the 
basis  of  all  fuels,  and  is,  therefore,  our  chief  heat-producing 
agent. 

Varieties  of  Carbon — Carbon  occurs  in  three  distinct 
states  which  do  not  bear  much  resemblance  to  each  other,  and 
which  are  known  as  allotropic  modifications. 

In  a  highly  crystalline  form  it  appears  as  the  diamond,  where 
it  is  the  hardest  substance  known.  It  is  clear,  transparent  and 
highly  refractive  to  light  rays.  It  is  not  affected  by  ordinarily 
high  temperatures  when  out  of  contact  with  oxygen.  In  the 
electric  arc,  it  softens,  swells  and  forms  black  coke.  When 
heated  in  the  presence  of  oxygen  it  burns  to  CO2. 

As  a  semi-crystalline  substance,  carbon  appears  in  the  form 
of  graphite,  plumbago  or  black-lead.  Graphite  is  used  to  make 
lead  pencils  and  "  black-lead  "  crucibles  for  melting  metals.  It 
is  largely  in  the  form  of  graphite  that  carbon  appears  in  pig  iron. 
The  amorphous  or  non-crystalline  variety  of  carbon  is  the  form 
that  most  interests  the  metallurgist.  This  variety  includes  hard 
coal,  coke  and  charcoal.  The  soft  coals  also  contain  from  50  to 
75  per  cent,  of  carbon,  and  from  20  to  40  per  cent,  of  combustible 
gases.  These  gases  also  contain  a  large  percentage  of  carbon 
combined  with  hydrogen,  and  are  generally  known  as  hydrocar- 
bon gases.  The  chief  of  these  hydrocarbon  gases  are, 


Some  Principles  of  Chemistry  and  Physics.  339 

Methane,  or  marsh  gas,  having  the  formula,  CH4,  and 
Ethylene,  or  olefiant  gas,  having  the  formula,  C2H4. 
Oxides  of  Carbon — Carbon  has  a  strong  affinity  for  oxy- 
gen at  elevated  temperatures.  When  burned  in  the  presence  of  air 
or  free  oxygen  it  is  capable  of  forming  two  oxides,  CO,  known  as 
carbonous  oxide  or  carbon  monoxide,  and  CO2,  known  as  carbonic 
acid,  carbon  dioxide  or  carbonic  anhydride.  Both  CO  and  CO0 
are  fixed  gases,  transparent  and  invisible,  but  they  differ  radically 
in  character.  CO  is  an  unsaturated  compound,  capable  of  taking 
up  another  atom  of  oxygen  and  forming  CO2.  In  other  words, 
it  is  combustible.  It  burns  with  a  blue  flame  which  is  familiar  to 
us  in  hard  coal  or  coke  fires,  giving  very  little  light  but  much  heat. 
It  is  extremely  poisonous  when  inhaled  and  is  responsible  for  the 
many  deaths  through  asphyxiation,  CO2,  on  the  other  hand,  is  a 
completely  saturated  compound  and  can  take  up  no  further  addi- 
tions of  oxygen.  It  is  therefore  incombustible.  It  is  a  heavy  gas, 
being  about  il/2  as  heavy  as  air.  It  has  a  tendency  to  collect  in 
depressions  in  the  earth,  such  as  caves,  wells,  enclosed  valleys, 
etc.,  and  while  it  is  not  poisonous,  it  is  a  source  of  danger  to  men 
or  animals  entering  such  depressions.  Continued  stay  in  its  pres- 
ence will  result  fatally,  as  it  will  not  support  life  or  combustion. 

Combustion  of  Carbon. — Carbon,  in  order  to  burn  to  the 
condition  of  CO2,  must  have  air  equal  to  or  in  excess  of  the  re- 
quirements indicated  in  the  equation, 

C  +  O2  =  CO2. 

Free  access  of  air  always  gives  CO2  as  the  product  of  burning 
carbon.  In  forming  CO2,  carbon  gives  up  all  of  the  heat  of  which 
it  is  capable.  It  has  been  determined  that  pure  carbon,  burning  to 
CO2  gives  approximately  14,550  British  Thermal  Units,  that  is, 
one  pound  of  carbon  burned  to  CO2  will  raise  14,550  pounds  of 
water  I  degree  F.  in  temperature.  When  carbon  is  burned 
with  an  insufficient  supply  of  oxygen  some  CO  is  formed,  the 
amount  depending  upon  the  degree  of  insufficiency.  When  there 
is  present  just  half  the  amount  of  oxygen  chat  is  needed  to  form 
CO2,  the  whole  of  the  product  of  combustion  of  carbon  will  be 
CO,  thus, 

2C  +  O2  =  2CO. 
It  has  been  determined  that  carbon,  burning  to- the  condition  of 


340  Blast  Furnace. 

CO,  develops  4450  B.  T.  U.,  which  is  only  about  30  per  cent,  of 
the  possible  total  when  the  combustion  is  complete.  Incomplete 
combustion  of  fuel,  therefore,  is  evidently  very  uneconomical. 
CO,  however,  is  a  combustible  gas,  and  is  capable  of  taking  up 
another  atom  of  oxygen.  In  doing  so,  each  pound  of  carbon 
gives  out  10,100  B.  T.  U.,  which  is  the  other  70  per  cent,  not 
developed  during  the  formation  of  CO.  It  appears,  therefore, 
that  owing  to  the  absorption  of  the  latent  heat  of  gasification  the 
addition  of  one  atom  of  oxygen  develops  far  more  heat  in  one 
case  than  in  the  other.  This  unequal  development  of  heat  has 
certain  advantages.  If  a  gaseous  fuel  is  desired,  it  may  pay 
to  sacrifice  30  per  cent,  of  the  heat  in  coal  in  order  to  develop  a 
combustible  gas  which  still  holds  in  a  potential  state  70  per  cent, 
of  the  original  heat  of  the  coal.  This  idea  forms  the  basis  of  the 
widespread  practice  of  converting  coals  into  producer  gases  for 
combustion  in  gas-burning  furnaces. 

Carbon  Transfer. — Carbon  monoxide  may  be  produced 
from  carbon  without  the  intervention  of  air  or  free  oxygen. 
When  CO2  is  brought  into  contact  with  carbon  which  is  heated  to 
redness,  a  portion  of  the  carbon  is  dissolved  by  the  second  atom 
of  oxygen  which  forms  the  CO2,  and  CO  is  the  result,  as  indicated 
in  the  following  reaction, 

CO2  +  C  =  2CO. 

This  is  a  refrigerating  or  endothermic  action,  owing  to  the  fact 
that  10,100  B.  T.  U.  is  absorbed  in  separating  the  oxygen  from 
the  CO2,  and  only  4450  B.  T.  U.  is  liberated  when  it  combines 
with  the  fresh  carbon.  Such  a  reaction  cannot  continue  long  un- 
less heat  be  supplied  from  some  external  source. 

Carbon  as  Reducing  Agent — As  a  reducing  agent  in  metal- 
lurgical operations,  carbon  has  a  value  second  only  to  its  worth 
as  a  fuel.  Its  power  to  act  simultaneously  as  a  producer  of  heat 
and  as  a  reducing  agent  makes  it  a  prime  requisite  to  the  smelter. 
At  temperatures  above  700  degrees  F.,  solid  carbon  has  the  power 
of  extracting  oxygen  from  oxides  of  iron,  thus, 

Fe208  +  3C  =  Fe2  +  3CO, 

but  as  the  reduction  of  iron  ore  is  pretty  well  completed  by  the 
time  it  reaches  that  temperature,  it  follows  that  the  above  reac- 


Sonic  Principles  of  Chemistry  and  Physics.  341 

tion  is  not  very  important  to  the  iron  smelter.  Nevertheless,  car- 
bon is  the  chief  reducing  agent  in  the  manufacture  of  pig  iron, 
but  it  is  in  the  form  of  CO  that  it  is  most  active.  CO  is  capable 
of  taking  up  oxygen  from  some  ores  of  iron  at  temperatures  as 
low  as  400  degrees  F.  It  is  the  power  to  act  at  such  low  temper- 
atures that  enables  it  to  have  the  reduction  nearly  done  before 
the  solid  carbon  can  act.  The  action  of  CO  upon  oxide  of  iron 
may  be  represented  thus, 

Fe203  +  3CO  ==  Fe2  +  3CO2, 

although  the  action  is  not  as  complete  as  this  equation  would  in- 
dicate. The  heat  evolved  by  this  reaction  more  than  balances 
that  absorbed,  and  hence  the  reaction  is  exothermic. 

IRON.      FE. 

Iron  is  an  element  that  is  familiar  to  all.  It  is  naturally  a  soft, 
tough,  fibrous  metal  when  pure,  as  in  wrought  iron  or  soft  steel. 
When  alloyed  with  small  quantities  of  carbon,  however,  it  be- 
comes harder  and  less  tough,  as  when  it  appears  in  the  form  of 
steel.  When  it  is  alloyed  with  3  to  4  per  cent,  of  carbon  and  al- 
most as  much  silicon,  together  with  other  elements,  such  as  phos- 
phorus, sulphur  and  manganese,  we  have  the  familiar  form  of 
cast  iron,  which  differs  very  widely  from  the  natural  metal. 

Oxides  ol  Iron. — Like  other  metals,  iron  readily  forms 
oxides  and  salts.  It  is  very  susceptible  to  the  attack  of  oxygen, 
and  forms  oxides  even  at  ordinary  temperatures.  The  oxide  is 
commonly  called  rust.  The  usual  red  iron  rust  is  the  sefq  uioxide 
of  iron,  Fe2O3,  usually  called  ferric  oxide.  This  compound  in 
the  form  of  ore  is  the  source  of  about  80  per  cent,  of  the  iron 
produced  in  the  world.  Besides  the  ferric  oxide,  a  ferrous  oxide, 
FeO,  is  found  in  combination,  although  it  cannot  be  isolated.  It 
is  in  this  form  that  iron  is  generally  present  in  blast  furnace  slags. 
Iron  forms  also  aferro-ferric  oxide,  Fe3O4,  which  is  magnetic  and 
is  practically  identical  with  roll  scale  and  magnetic  iron  ore. 

SILICON,    si. 

Next  to  oxygen,  silicon  is  the  most  abundant  element  in  the 
earth.  Nevertheless,  comparatively  few  persons  are  familiar  with 
its  appearance.  This  is  due  to  the  fact  that  it  clings  very  tena- 


342  Blast  Furnace. 

ciously  to  its  compounds  and  is  rarely  isolated.  It  is  said  to  occur 
in  three  modifications,  like  carbon.  The  amorphous  variety  is  a 
brown  powder  which  burns  readily  in  air. 

Silica. — Silicon  forms  one  oxide,  silicon  anhydride,  or  silica, 
having  the  formula  SiO2.  The  attraction  between  silicon  and 
oxygen  is  very  strong,  and  much  heat  is  given  out  during  the 
combustion.  Pure  silica  is  a  white,  earthy  substance  and  occurs 
in  nature  as  quartz,  rock-crystal  and  fine,  white  sand.  When 
colored  by  iron  or  other  metals  it  appears  as  flint,  jasper,  agate  and 
some  of  the  precious  and  ornamental  stones.  Combined  with  vari- 
ous bases  it  is  the  chief  component  of  all  igneous  rocks  and  also 
of  all  manufactured  and  natural  glass.  It  is  usually  the  chief 
acid  factor  of  metallurgical  slags,  and  the  chief  ingredient  of  re- 
fractory firebricks. 

Silicon  in  Pig  Iron. — During  the  smelting  of  iron,  various 
quantities  of  silicon  are  reduced  from  the  silica  and  alloy  with  the 
iron.  The  effects  of  this  silicon  upon  the  quality  of  pig  iron  have 
an  enormous  bearing  upon  the  merallurgic  art. 

ALUMINUM.       AL. 

Aluminum  is  in  some  ways  related  to  silicon.  While  it  is  not 
as  abundant  as  silicon,  yet  they  are  generally  associated  in  nature, 
and  so  occur  together  in  artificial  products  that  are  obtained  from 
earthy  materials.  In  this  way  aluminum  in  its  oxidized  form  enters 
largely  into  the  composition  of  slags.  Alu'minum  is  a  metal,  and 
its  oxide,  A1,O3  is  generally  considered  a  base  and  may  unite 
with  silica,  forming  silicates  of  aluminum,  such  as  clay.  Yet 
when  there  is  a  plenitude  of  other  bases  and  a  scarcity  of  silica, 
alumnic  oxide  appears  to  have  the  faculty  of  acting  as  an  acid, 
as  it  assists  the  silica  in  assimilating  the  bases. 

Alumina. — Aluminum  forms"*one  oxide,  A12O3,  which  is 
called  alumina.  It  is  a  hard,  granular  substance  much  like  silica, 
and  occurs  in  nature  as  corundum,  ruby,  emerald,  etc.  It  occurs 
also  in  most  igneous  rocks  and  is  the  essential  ingredient  of  all 
clays. 

CALCIUM.      CA. 

Calcium  is  a  yellowish-white  metal,  which  owing  to  its  strong 
affinity  for  oxygen  is  difficult  to  reduce  and  is  rarely  seen  in  its 


Some  Principles  of  Chemistry  and  Physics.  343 

elemental  form.  Its  properties  are  not  such  as  to  make  it  espe- 
cially useful,  and  therefore  there  is  no  incentive  to  separate  the 
metal.  It  has  its  greatest  usefulness  when  in  the  form  of  its 
oxide. 

Lime — Calcium  is  bivalent  and  forms  one  oxide,  CaO.  This 
compound  is  the  familiar  substance  which  is  called  lime,  and  is 
used  largely  in  agricultural  and  building  pursuits.  It  is  made  by 
heating  limestone,  CaCO3,  to  high  temperatures.  The  CO2  is 
liberated  by  the  heat,  and  the  CaO  is  left  behind  in  white,  friable 
lumps,  which  is  known  as  burnt  lime  or  quicklime.  When  this  is 
exposed  to  the  air  for  considerable  periods  it  absorbs  moisture 
and  falls  to  powder.  It  is  then  known  as  slacked  lime.  A  clear 
solution  of  lime  in  water  is  used  as  medicine  under  the  name  of 
limewater.  When  mixed  with  quantities  of  water  insufficient  for 
complete  solution,  it  is  known  as  milk  of  lime.  When  limestone 
is  used  as  a  furnace  flux,  the  CaO  is  the  base  which  unites  with 
the  siliceous  gangue  to  form  the  slag. 

MAGNESIUM.       MG. 

Magnesium  is  a  white,  lustrous  metal,  which  burns  readily 
in  air  with  a  dazzling  white  light.  It  is  the  basis  of  all  flash- 
light preparations  for  photographic  work.  Magnesium  and  its 
compounds  resemble  closely  those  of  calcium.  They  both  belong 
to  a  group  of  elements  known  as  the  alkaline  earths.  Magnesium 
occurs  in  nature  in  large  quantities  as  magnesite,  MgCO3,  and  as 
dolomite,  Mg(Ca)CO3.  Both  substances  when  calcined  are  large- 
ly used  as  refractory  materials  for  lining  steel-making  furnaces. 
In  the  form  of  dolomite  magnesium  enters  the  blast  furnace  as 
flux,  where  in  the  form  of  MgO  it  replaces  some  of  the  CaO  in 
the  slag. 

Magnesia — Magnesium  forms  one  oxide  called  magnesic 
oxide,  or  magnesia,  MgO,  which  is  metallurgically  its  most  im- 
portant compound.  It  is  a  white  solid  and  is  the  product  alike  of 
the  'combustion  of  flashlight  powder  and  of  the  calcination  of 
magnesite. 

MANGANESE.       MN. 

Manganese  is  a  metal  of  grayish-white  color,  hard  and  brittle. 
It  alloys  readily  with  iron,  and  is  generally  produced  as  such  an 


344  Blast  Furnace. 

alloy.  Its  uses  are  mainly  confined  to  its  alloys,  as  the  pure  metal 
does  not  possess  the  usual  qualities  desirable  in  a  metal.  Its  most 
used  alloys  are  spiegeleisen  and  ferromanganese,  which  are  uni- 
versally employed  in  steel  manufacture. 

Oxides  of  Manganese — Manganese  forms  several  oxides. 
MnOo,  manganese  dioxide,  is  its  chief  ore.  MnO,  manganic 
oxide,  is  the  form  in  which  it  enters  into  combination  with  silica 
in  slags. 

THE  ALKALIS.       NA  AND  K. 

Sodium — Sodium  is  a  soft,  silvery  white  metal,  which  can- 
not exist  either  in  air  or  in  water.  Its  most  usual  compound  is 
the  chloride  which  is  our  common  salt.  Its  hydrate  is  largely 
used  in  making  soap  and  its  silicates  in  making  glass. 

Potassium. — Closely  related  to  and  resembling  sodium  is  the 
metal  potassium.  They  frequently  occur  together  and  their  com- 
pounds are  used  for  similar  purposes,  hence  they  are  often  classed 
together  as  the  alkalis.  They  both  occur  in  small  quantities  in 
the  ash  of  coal  and  wood  and  sometimes  in  the  gangue  of  ores  and 
limestone.  Thus  they  find  their  way  into  blast  furnace  slags 
in  small  quantities.  The  alkalis  show  an  especial  affinity  for 
cyanogen,  and  the  resulting  alkaline  cyanides  are  supposed  to 
have  considerable  effect  upon  the  reactions  in  the  furnace. 

PHOSPHORUS.    P. 

Phosphorus,  when  pure,  is  a  colorless,  transparent,  wax-like 
substance.  When  heated  gently  out  of  contact  with  the  air,  it 
changes  to  an  allotropic  condition  known  as  red  phosphorus.  It 
unites  readily  with  oxygen,  being  very  inflammable,  and  hence 
finds  wide  use  in  the  manufacture  of  matches.  It  occurs  in  nature 
chiefly  as  calcic  phosphate,  and  as  such  is  largely  used  as  a  fertil- 
izer. The  universal  presence  of  phosphates  in  all  the  materials 
which  go  to  make  up  a  furnace  charge  makes  phosphorus  an  im- 
portant element  from  a  metallurgical  standpoint. 

Oxides  of  Phosphorus. — Phosphorus  forms  several  oxides 
according  to  the  degree  of  oxidation.  The  chief  oxides  are  phos- 
phoric anhydride,  P2O5,  sometimes  called  the  pentoxide,  and  phos- 
phorus anhydride,  P2O3,  known  also  as  the  trioxide.  The  oxides 
of  phosphorus  are  acid  radicals,  and  demand  basic  associates,  yet 


Some  Principles  of  Chemistry  and  Physics.  345 

their  affinity  for  bases  is  not  so  strong  as  that  of  silica,  and  there- 
fore they  arc  readily  displaced  by  silica  in  slags.  The  displaced 
oxides  are  readily  reduced  and  the  phosphorus  is  found  in  the 
iron  in  consequence.  Very  basic  slags  are  capable  of  holding 
phosphorus,  but  blast  furnace  slags  are  rarely  sufficiently  basic  to 
do  so. 

SULPHUR.       S. 

Sulphur  at  ordinary  temperatures  is  a  brittle  solid  of  light  yel- 
low color,  but  at  higher  temperatures  takes  on  allotropic  modifi- 
cations. It  burns  freely  in  air  but  is  less  inflammable  than  phos- 
phorus. It  forms  two  oxides,  SO2,  sulphuric  dioxide  and  SO3, 
sulphuric  trioxide.  or  anhydride.  Both  substances  are  volatile  at 
ordinary  temperatures,  but  are  quite  irrespirabk,  and  are  largely 
used  for  killing  disease  germs  by  fumigation.  Sulphur  is  the  basis 
of  sulphuric  acid,  and  a  very  large  class  of  compounds  known  as 
sulphates. 

Sulphur  occurs  in  ores  usually  in  the  form  of  iron'  pyrites, 
FeS2,  a  brassy  looking  mineral,  showing  bright,  crystalline  facets. 
It  always  acts  as  an  acid  radical  whether  in  the  elemental  or  oxi- 
dized condition.  The  element  as  well  as  its  oxides  is  volatile.  All 
of  these  conditions  have  a  bearing  on  the  action  of  sulphur  in 
the  hearth  of  a  blast  furnace. 

Since  elemental  sulphur  is  an  acid  radical,  it  may  or  may  not 
enter  the  iron.  Unlike  the  other  elements  it  may  unite  directly 
with  calcium,  forming  CaS,  and  enter  the  slag.  Its  oxides  are 
always  found  in  the  slag.  The  quantity  of  sulphur  that  may 
enter  the  slag  varies  with  the  quantity  of  lime  present,  hence  the 
amount  of  lime  used  has  an  important  influence  upon  the  quantity 
of  sulphur  entering  pig  iron. 

Since  sulphur  and  its  oxides  are  volatile  at  high  temperatures, 
it  follows  that  a  very  hot  hearth  will  retain  less  sulphur  in  its 
pig  iron  than  a  cold  one.  These  two  factors,  heat  and  lime,  are 
the  means  for  controlling  the  quantity  of  sulphur  in  pig  iron. 


346 


Blast  Furnace. 


CERTAIN   ELEMENTS   AND   SOME  OF   THEIR   PROPERTIES. 


Calculated  by 

F.  W.  Clark, 

Bulletin  78, 

|U.  S.  Geol.  Sur. 

pp.  34-43. 


"8      ^ 

£          o 

1 

"N 

0-£ 

lg— 

> 

^i 

o 

-M 

pl«l 

1 

I 

a 

1  = 

•2  j> 

'C  cS 

F.    - 

rl 

Is 

•3 

pi 

£ 

55 

g* 

-<  "* 

£M 

5'  W 

c'^ 

^ 

Gas  

,  .  .  .  Hydrogen 

H 

1 

1 

H2O 

Colorless  llo. 

IS 

62,000 

Metalloid 

Carbon  

.C 

12 

2 

CO 

Colorless  gas. 

28 

4^450 

Metalloid 

.  .  .  .Carbon  

.C 

12 

4 

C02 

Colorless  gas. 

44 

14,550 

Gas  

.  .  .   Nitrogen 

N 

14 

£ 

* 

* 

* 

* 

Cas. 

.  .      Oxygen 

o 

16 

2 

Metal 

Sodium 

Na 

23 

o.;»7 

1 

Xa-.O 

i 

62 

3,950 

Metal 

Me 

24 

1  .74 

MgO 

White   solid. 

40 

10,755 

Metal 

\luminum 

•  *••!& 
.  .Al 

or 

2.67 

3 

White   solid. 

102 

13,086 

Metalloid 

Silicon  

.Si 

28 

4 

SiO2 

White  solid. 

60 

11^571 

Metalloid 

.  .  .  .Phosphorus. 

.  P 

31 

5 

P205 

White  solid. 

142 

10,605 

Metalloid 

.  .  .  .Sulphur.  .  .  . 

.S 

32 

4 

SO2 

Pungent  gas. 

64 

3,896 

Metal 

Potassium 

.  .K 

39 

0.86 

-« 

T^  O 

j. 

94 

2,266 

"Metal 

Calcium 

.  .Ca 

40 

1.58 

2 

CaO 

White  solid. 

56 

5,917 

Metal 

....  Alanganes^  . 

.  Mn 

8.00 

2 

MnO 

71 

2,975 

Metal.  . 

.  .  .  .Manganese. 

.  Mn 

55 

4 

MnO2 

Black    solid. 

87 

4,100 

Metal  

....  I  ron  ... 

Fe 

56 

7.90 

2 

FeO 

TO 

2,111 

Metal 

.  .  I  ron  

.  .Fe 

56 

3 

Fe2O3 

Red  solid 

160 

3,144 

Metal 

Iron 

Fe 

56 

2&4 

Fe3O4 

Grav-black 

232 

2  900 

*  Forms  several  oxides  at  different  valencies, 
t  Occurs  only  in  combination. 

PARTIAL  COMPOSITION  OF  EARTH'S  CRUST  BY  WEIGHT. 

(Showing  the  Relative  Proportion  of  Different  Elements  Present.) 


Par  cent. 

Oxygen   49.98 

Silicon    25.30 

Aluminum    7.26 

Iron 5.08 

Calcium 3.51 

Magnesium 2.50 

Sodium   ....  .    2.28 


Per  cent. 

Potassium   2.23 

Hydrogen   '.  .    0.94 

Titanium    0.30 

Carbon    0.21 

Phosphorus    0.09 

Manganese   0.07 

Sulphur   0.04 


PHYSICAL  CHANGES  OF  MATTER. 

While  chemical  change  plays,  as  we  have  seen,  a  very  im- 
portant  part  in  the  metallurgy  of  iron,  yet  it  is  so  interwoven  with 
physical  change  that  it  would  not  be  a  simple  matter  to  draw  the 
line  sharply  between  the  respective  utilities  of  the  two.  The 
study  of  blast  furnace  phenomena  would  be  very  incomplete  if  it 
did  not  include  a  study  of  some  of  the  physical  changes  of  matter, 
particularly  those  of  air  and  some  of  the  fixed  gases  which  are  so 
closely  connected  with  the  process  of  combustion. 


Some  Principles  of  Chemistry  and  Physics.  347 

PHASES   OF    MATTER. 

All  matter  is  supposed  to  be  capable  of  assuming  the  three  con- 
ditions or  phases,  viz.,  solid,  liquid  and  gaseous.  Those  sub- 
stances which  appear  to  us  as  solids  at  ordinary  temperatures,  may 
be  made  liquid  or  gaseous  by  a  sufficiently  elevated  temperature. 
Generally  liquids  may  be  frozen  into  solids  or  converted  into 
vapors,  and  gases  may  be  condensed  to  liquid  and  solid  forms. 
The  state  which  we  associate  with  familiar  objects  is,  therefore, 
not  necessarily  the  only  one  inherent  in  them,  but  merely  the  one 
in  which  they  exist  at  ordinary  temperatures.  Some  substances 
are  made  to  assume  other  states  only  by  intense  extremes  of  tem- 
perature. For  example,  iron  at  ordinary  temperatures  is  solid. 
To  make  it  liquid  requires  a  temperature  of  more  than  2500  de- 
grees F.,  and  to  render  it  volatile  requires  a  much  higher  tempera- 
ture. On  the  other  hand,  some  substances,  such  as  water,  for 
example,  are  capable  of  assuming  all  three  states  within  a  com- 
paratively narrow  range  of  temperature.  At  ordinary  tempera- 
tures water  is  a  liquid,  at  32  degrees  F.  it  is  ice,  and  at  212  degrees 
F.  it  is  turned  into  yapor.  Such  changes,  it  must  be  remembered, 
are  merely  physical  and  do  not  at  all  affect  the  composition  of  the 
substance. 

THE   PHASE   LAW. 

Every  substance,  whether  in  the  state  of  solid,  liquid  or  gas,  is 
subject  to  three  variables,  whose  effects  are  mutually  interde- 
pendent, viz. :  temperature,  pressure  and  volume.  When  the  sub- 
stance is  present  in  only  one  state  or  phase,  two  of  the  variables 
must  be  fixed  upon  before  the  third  can  be  determined.  The 
third  follows  as  a  consequence  of  the  two  which  are  fixed.  For 
example,  a  given  weight  of  gas  may  be  known  to  have  a  certain 
temperature,  but  its  pressure  and  volume  will  still  be  indetermin- 
ate and  subject  to  mutual  variations.  If,  however,  a  given  pres- 
sure is  also  fixed  upon,  the  gas  will  necessarily  occupy  a  certain 
definite  volume,  or  if  its  volume  can  be  fixed,  its  pressure  can  be 
determined.  The  gas  is,  therefore,  said  to  have  two  degrees  of 
freedom,  and  this  statement  is  true  of  every  uniform  substance 
when  present  in  only  one  phase. 

With  the  addition  of  each  phase,  however,  the  number  of  de- 


348  Bias'  Furnace. 

grees  of  freedom  is  reduced  by  one.  When  two  phases  are  present 
the  fixing  of  one  variable  determines  the  other  two.  For  example, 
if  water  and  its  vapor  exist  in  contact  at  atmospheric  pressure,  a 
definite  volume  of  vapor  will  form  at  that  temperature.  If  now, 
the  pressure  be  diminished,  for  example,  additional  vapor  can 
form  and  the  temperature  will  fall  and  equilibrium  be  established 
again  at  larger  volume  and  lower  temperature.  When  ice, 
water,  and  water  vapor  are  present,  there  are  no  degrees  of 
freedom,  as  they  can  exist  simultaneously  only  at  one  temperature, 
pressure  and  volume.  The  addition  of  other  substances,  however, 
adds  a  degree  of  freedom  for  each  new  component.  With  two 
components,  such  as  water  and  alcohol  the  presence  of  two  phases 
still  permits  two  degrees  of  freedom,  in  accordance  with  the  fol- 
lowing Phase  Law : 

No.  phases  -)-  no.  deg.  freedom  =  no.  components  +  2, 
which  is  true  for  any  number  of  components  and  phases.  This  is 
a  natural  consequence  of  Dalton's  Law  of  Partial  Pressures, which 
states  that  in  any  volume  of  mixed  gases  each  gas  acts  independ- 
ently of  every  other  as  if  it  filled  the  entire  space  alone,  and  the 
pressure  it  exerts  is  therefore  in.  proportion  to  the  quantity  pres- 
ent. The  sum  of  the  partial  pressures  of  the  gases  present  is  al- 
ways equal  to  the  whole  pressure  exerted  by  the  mixture. 

THE   STATES  OF   MATTER. 

As  already  stated,  all  matter,  in  whatever  phase  it  occurs,  is 
made  up  of  minute  particles  styled  "  molecules."  These  mole- 
cules are  held  together  by  a  mutual  attraction  which  is  usually 
designated  as  "cohesion."  The  strength  of  this  force  is  always 
the  same  for  any  given  substance  under  given  conditions,  but  it 
varies  widely  for  different  substances  and  also  for  the  same  sub- 
stances under  different  conditions.  Indeed,  the  striking  differ- 
ences between  the  various  phases  of  a  given  substance  are  due 
chiefly  to  difference  in  cohesion. 

Solids. — The  solid  state  of  matter  is  always  characteristic  of 
its  lower  temperatures  and  appears  to  have  the  cohesive  force 
more  marked  than  that  of  the  other  phases.  It  is  always  charac- 
terized by  comparative  rigidity  and  tenacity  and  is  not  readily 
changed  in  shape  without  fracture.  This  condition  is  attributed  to 


Some  Principles  of  Chemistry  and  Physics.  349 

the  pressure  of  a  rigid,  inflexible  state  of  the  cohesion,  which 
does  not  permit  of  distortion  without  rupture.  Yet  the  molecules 
are  supposed  to  be  separated  from  each  other  and  are  capable  of 
free  motion  within  a  certain  radius. 

Liquids. — The  liquid  state  of  matter  usually  follows  when 
the  solid  phase  is  subjected  to  a  sufficiently  high  temperature.  It 
is  characterized  by  greater  mobility,  enabling  it  to  change  shape 
readily  without  fracture  and  to  conform  accurately  to  the  inte- 
rior of  any  containing  vessel.  This  condition  is  attributed  to  less- 
ened cohesive  force,  which  enables  the  molecules  to  slide  readily 
over  each  other  without  actual  rupture.  The  molecules  are  some- 
what more  separated  and  vibrate  with  much  greater  activity.  Yet 
the  volume  and  specific  gravity  are  usually  not  very  different  in 
the  two  phases,  the  liquid  having  a  slightly  greater  specific  weight 
than  the  solid. 

The  change  from  the  solid  to  the  liquid  state  of  a  uniform 
substance  always  takes  place  at  a  constant  temperature,  which  is 
known  as  the  melting  point.  In  addition  to  the  sensible  heat  which 
it  is  necessary  for  the  substance  to  absorb  before  it  can  become 
liquid,  an  amount  of  heat  peculiar  to  each  substance  is  rendered 
latent,  and  is  known  as  the  latent  heat  of  fusion.  This  heat  does 
not  appear  as  an  increase  of  temperature  of  the  substance,  but  is 
used  up  in  separating  the  molecules  and  otherwise  maintaining 
the  state  of  liquidity. 

Oases — The  gaseous  state  of  matter  usually  results  from 
the  further  application  of  heat  to  the  liquid  phase.  A  limited 
quantity  of  vapor  may  usually  be  induced  by  simply  decreasing 
the  pressure  without  change  of  temperature.  The  vaporous  state 
is  characterized  by  extreme  tenuity,  great  volume  and  low  specific 
gravity.  The  cohesive  force  of  the  substance  appears  to  be  entire- 
ly destroyed  and  separation  may  occur  through  its  own  expansive 
energy.  Under  ordinary  conditions,  vapor  may  form  on  the  sur- 
face of  a  liquid  until  its  density  counterbalances  the  tendency  to 
form  vapor.  This  tendency  is  known  as  the  vapor  pressure  of  the 
liquid.  The  vapor  pressure  increases  rapidly  with  the  tempera- 
ture of  the  liquid  and  when  it  exceeds  the  pressure  of  the  super- 
imposed atmosphere,  vapor  is  given  off  rapidly  and  the  liquid  is 
said  to  "boil."  This- temperature  is  called  the  boiling  point.  For 


350 


Blast  Furnace. 


any  given  substance  the  boiling  point  is  constant  under  given  con- 
ditions. Changes  of  superimposed  pressure,  however,  affect  this 
temperature,  depressing  it  when  the  pressure  is  decreased,  and 
raising  it  when  the  pressure  is  increased.  For  example,  in  the 
case  of  water, 

At  sea  level,  under  an  atmos.  pros,  of  30  in.  Mer.,  it  boils  at  212°  F. 
At  1,800  ft.  elevation,  under  an  atmos.  pres.  of  28  in.  Mer.,  it  boils  at  208°  F. 
At  4,700  ft.  elevation,  under  an  atmos.  pres.  of  25  in.  Mer.,  it  boils  at  203°  F. 
At  10,600  ft.  elevation,  under  an  atmos.  pres.  of  20  in.  Mer.,  it  boils  at  192°  F. 

As  in  the  case  of  fusion,  the  change  of  state  from  liquid  to 
vapor  is  accompanied  by  an  absorption  of  sensible  heat  which 
raises  the  temperature  of  the  substance,  and  also  of  latent  heat 
which  supplies  the  energy  that  effects  the  change  of  state'.  The 
latter  is  known  as  the  latent  heat  of  vaporization.  In  putting  the 
substance  through  the  reverse  changes  the  latent  heats  are  again 
converted  into  sensible  heat  and  radiated  by  the  substance. 

SPECIFIC  HEATS  OF  CERTAIN  SUBSTANCES. 


Substance, 
Water. .  . 


Temper-         Quantity  of  heat 
atures.          needed  to  raise  1 
Deg.  F.     pound  from  0°  to  t°  F. 
.32  to  212        1. Of +0.0001 5t2 


Steam 212  to  3,600  0.42/+0.000185/2 

CO Up  to  3,600 

CO Up  to  3,600 

°* Up  to  3,600 

Calculations,"     N2 Up  to  3,600 

pp.  60-98  inc.     H2 Up  to  3)6oo 

Air Up  to  3,600 

MgO Up  to  3,600 

A12OS Up  to  3,600 

SiO2 Up  to  3,600 

CaO Up  to  3,600 

Fe2O3 Up  to  3,600 


Quantity  of 
heat  needed  to  raise 
1  pound  from  t° — ti°  F. 
!.()(*— t,)  4-0.0001 5  (t2—  *j2) 
0.42U— *i)  +0.000185  (ts—tls) 

0.2405/+0.000021 43i2    0.2405  ( t—tt )  +0.000021 43 ( t- — /r 
0.1870/+0.0()01.m2         0.1870  (  *— M+0.000111  <  *-— V) 
0.2104 ( t—  «!)+0.00001875 ( f 2— «r 
0.2405  (t—ti)  +0.00002143  (t-—^ 
3.367  ( t—t! )  +0.0003  ( t2— V) 
0.2335  U— *i)  +0.0000208  ( <-— V) 
0.242  ( t — ti)  +0.000016  ( t- — if  > 
0.208  ( t—ti )  +0.0000876  ( t  -—  1  r) 
0.1833  (t — *i)  +0.000077  (t- — <i!) 
0.1715  ( t—t^  +0.00007  ( t2—  <r ) 
0.1456  ( t — ti)+0.000188  ( t- — V) 


0.2104*+0.00001875£2 

0.2405/+0.00002143*2 

3.367*+0.0003<2 

0.2335f+0.0000208f- 

0.242t+0. 00001  Qt- 

0.208M-0.0000876*2 

0.1833f+0.000077/2 

0.1715t+0.00007t2 


0.1456f+0.000188t- 

The  coefficients  of  thermal  capacity  per  cubic  foot  of  the  above  gases  may  be 
found,  if  desired,  by  dividing  the  above  coefficients  per  pound  by  the  number  of 
cubic  feet  which  1  pound  of  the  gas  occupies  at  32  degrees  F. 

THERMAL  PROPERTIES  OF  CERTAIN   METALS. 


Metal. 
Sodium                   •  •  • 

Melting  point. 
Deg.  F. 
206 

Latent  heat 
Latent  heat                                    of  vapor- 
of  fusion.        Boiling  point.         ization. 
B.  T.  IT.                 Deg.  F.                B.  T.  U. 
57                       1,368                       1,827 
104                       1,980                       2,367 
180                       4,172                       4.100 
230                       5,072                       4,540 
9                          548                           185 
17                           832                           130 
951 
132  }-Not  readily  volatile. 
126  j 

....  1,157 

Silicon 

2,606 

...      Ill 

237 

1.436 

3,000 

Some  Principles  of  Chemistry  and  Physics.  351 

HEAT  OF  PHYSICAL  CHANGES. 

From  the  preceding  discussion  it  is  evident  that  in  causing 
matter  to  change  from  a  cold  solid  to  a  superheated  vapor  through 
the  application  of  heat,  there  will  ordinarily  be  five  distinct  quan- 
tities of  heat  required,  as  follows : 

1 i )  Heat  needed  to  raise  the  solid  phase  to  the  melting  point. 

(2)  Heat  rendered  latent  in  effecting  the  change  of  state  to 
liquid. 

(3)  Heat  needed  to  raise  the  liquid  to  the  boiling  point. 

(4)  Heat  rendered  latent  in  effecting  the  change  to  vapor. 

(5)  Heat  needed  to  superheat  the  vapor. 

As  already  stated,  the  latent  heat  is  the  quantity  of  heat  hy- 
pothecated by  the  substance  to  effect  the  change  of  state  from  one 
phase  to  another.  The  latent  heat  differs  for  different  substances, 
and  for  any  given  substance  the  heat  of  fusion  differs  from  that 
of  vaporization.  Usually  they  are  both  related  to  the  melting- 
point  and  boiling  point  respectively.  The  latent  heat  of  fusion 
of  elements  per  pound  corresponds  closely  to  the  formula, 

T  TT      _  2>I  X  T(mpt), 
*f~         Atomic  wt. 

where  T  (nipt)  =  the  absolute  temperature  F.  of  the  melting  Richards 
point.  The  latent  heat  of  vaporization  corresponds  closely  to  the  JJfjJ'S 
formula, 

LH    =  23XT(bpt) 
'v     '    Atomic  wt. 

where  T(bpt)  =  the  absolute  temperature  F.  of  the  boiling  point. 
The  quantity  of  heat  needed  to  raise  the  temperature  of  the 
substance  to  that  of  the  next  phase  depends  upon  its  thermal 
capacity,  which  also  varies  for  each  substance  and  for  each  phase 
of  the  substance.  The  coefficient  of  thermal  capacity  is  commonly 
called  ••  Specific  Heat,"  and  the  method  of  its  measurement  is 
based  upon  comparison  with  the  thermal  capacity  of  water.  The 
Engineers'  unit  of  heat  measurement  is  the  British  Thermal  Unit, 
usually  abbreviated  "  B.  T.  U."  One  B.  T.  U.  is  the  quantity  of 
heat  required  to  raise  one  pound  of  water  i  degree  F.  at  its  great- 
est density,  namely  39  degrees  F.  The  specific  heats  of  other  sub- 
stances also  are  the  quantities  of  heat,  measured  in  British  Ther- 


352  Blast  Furnace. 

mal  Units,  which  are  necessary  to  raise  their  temperatures  I  de- 
gree F.  As  the  thermal  capacity  of  water  is  greater  than  that  of 
most  substances,  it  follows  that  if  its  specific  heat  is  taken  as 
unity,  those  of  most  other  substances  will  be  expressed  by  frac- 
tions. The  coefficients  of  the  thermal  capacity  of  most  substances 
are  not  constant,  but  increase  slightly  as  the  temperature  of  the 
substances  rises. 

The  specific  heats  of  the  elements  bear  a  definite  relation  to 
their  atomic  weights.  It  was  observed  by  Dulong  and  Petit  in 
1818  that  the  product  of  the  atomic  weight  and  specific  heats  of 
the  elements  was  fairly  constant  at  about  6.4,  known  as  the  atomic 
heat.  It  is  supposed,  therefore,  that  equal  weights  of  all  atoms 
have  about  the  same  capacity  for  heat.  It  follo\vs,  consequently, 
that  an  element  with  a  low  atomic  weight  will  have  a  high  specific 
heat  and  vice  versa.  This  law  furnishes  a  means  of  calculating 
specific  heats  from  atomic  weights. 

The  atoms  appear  to  retain  their  original  atomic  heats  even 
when  in  combination,  ,and  hence  the  molecular  heats  of  compounds 
are  equal  to  the  sums  of  the  atomic  heats  of  elements  forming 
them.  Molecular  heats  of  similar  salts  are  virtually  the  same,  and 
in  simple  .compounds  are  usually  approximately  six  times  the 
number  of  atoms  involved. 

MOISTURE   IN   THE   ATMOSPHERE. 

All  liquids  and  some  solids  give  off  vapor  at  all  times,  the  quan- 
tity of  which  is  dependent  upon  the  temperature  and  the  quantity 
of  vapor  present.  The  presence  of  other  vapors  or  gases  has  no 
effect,  except  when  they  influence  the  temperature.  The  only 
pressure  which  appears  to  check  vaporization  is  that  exerted  by 
the  vapor  itself.  The  evaporation  of  water  is  a  case  in  point.  It 
is  customary  to  consider  that  the  water  vapor  is  taken  up  and 
held  in  suspension  by  the  air,  and  when  all  of  the  vapor  has 
formed  that  can  exist  at  a  given  temperature  we  are  accustomed 
to  say  that  the  air  is  saturated  with  vapor.  It  would  be  more 
nearly  correct,  however,  to  say  that  the  space  is  saturated  with 
vapor,  because  the  quantity  of  vapor  is  in  no  way  governed  by  the 
presence  of  air  except  in  so  far  as  the  air  influences  the  tempera- 
ture of  the  space.  The  same  amount  of  vapor  would  exist  at  the 


Some  Principles  of  Chemistry  and  Physics. 


given  temperature  if  the  air  were  wholly  absent.  The  capacity  of 
space  for  water  vapor  increases  rapidly  as  the  temperature  rises, 
and  the  vapor  pressure  of  the  liquid  follows  closely.  The  change 
is  very  slow  at  low  temperatures,  but  after  the  temperature  rises 
above  the  freezing  point  the  power  to  vaporize  increases  rapidly. 
This  tendency  is  illustrated  graphically  by  curves  (i)  and  (2)  on 
the  chart. 


-30        -20        -10 


0  10          20          30          40  50          60  JO          80          SO         100 

'TEMPERATURE  IN   DEGREES   FAHRENHEIT 


Chart  Showing  Effect  of  Temperature  on  Moisture  in  Air. 

When  water  vapor  forms  in  the  presence  of  air  it  permeates 
the  air  and  for  the  time  acts  as  an  integral  part  of  it.  Water 
vapor  has  only  63  per  cent,  of  the  weight  of  an  equal  volume  of 
dry  air  at  the  same  temperature.  Hence  a  cubic  foot  of  moist  air 
is  lighter  than  the  same  volume  of  air  would  be  if  dried.  When 
dry  air  takes  up  water  vapor,  however,  its  weight  is  increased  by 
just  the  weight  of  moisture  added.  At  the  same  time,  its  ex- 
pansive force  and  consequently  its  volume  is  increased,  so  that  the 
net  result  is  less  weight  per  cubic  foot  than  when  the  moisture  is 
absent.  If,  however,  the  moisture  could  be  removed  from  the  air 
without  change  of  volume,  the  air  so  desiccated  would  be  lighter. 
This  fact  is  shown  very  clearly  by  curves  (3)  and  (4)  of  the  ac- 
companying chart.  The  thin  wedge  between  the  two  lines  (3) 


354  Blast  Furnace. 

and  (4)  shows  the  relative  weight  of  the  moisture  and  that  of  the 
saturated  air. 

The  vaporization  of  water,  which  is  so  dependent  upon  high 
temperature,  tends  to  neutralize  its  own  activity  through  the  cool- 
ing effect  of  the  action  itself.  The  heat  absorbed  during  vaporiza- 
tion is  966  B.  T.  U.  per  pound,  of  which  894  B.  T.  U.  becomes 
latent  and  72  B.  T.  U.  is  used  up  in  expanding  the  vapor  against 
the  pressure  of  the  atmosphere.  This  quantity  of  heat  is  sufficient 
to  raise  the  temperature  of  more  than  5  pounds  of  ice  water  to  the 
boiling  point. 

FIXED  GASES. 

While  all  vapors  may  act  as  perfect  gases  when  at  tempera- 
tures well  above  the  boiling  point,  it  is  only  those  which  do  not  have 
to  be  induced  by  elevated  temperatures  but  whose  boiling  points 
He  well  below  ordinary  atmospheric  temperatures,  that  are  said 
to  be  permanent  or  fixed  gases.  Gases  are  usually  transparent, 
colorless  bodies  of  such  tenuity  as  to  offer  but  little  resistance 
to  motion.  They  are  very  light  yet  have  easily  measurable  weights 
and  a  given  volume  of  a  given  gas  at  a  given  temperature  will 
always  weigh  the  same.  Air,  for  example,  is  a  mixture  of  two 
permanent  gases  and  consequently  is  a  permanent  gas  also.  At 
62  degrees  F.  the  weight  of  I  cubic  foot  of  air  at  sea  level  is 
0.0761  pounds,  and  it  takes  13.14  cubic  feet  of  air  to  weigh  I 
pound  avoirdupois  at  that  temperature. 

Pressure  of  Atmosphere — The  mass  of  air  which  surrounds 
the  earth  exerts  a  pressure  due  to  its  weight,  equal  to  14.7  pounds 
at  sea  level  for  every  square  inch  of  the  earth's  surface.  This  is 
commonly  called  atmospheric  pressure,  and  is  usually  measured  by 
means  of  a  barometer  in  which  a  column  of  mercury  is  arranged 
to  just  balance  the  pressure  of  the  air.  At  sea  level  it  usually 
takes  from  29  to  30  inches  of  mercury,  according  to.  weather  con- 
ditions, to  balance  the  air,  which  corresponds  to  a  weight  of  14.2 
to  14.7  pounds  atmospheric  pressure.  At  greater  altitudes  the 
superincumbent  mass  of  air  is  less  and  the  pressure  is  correspond- 
ingly decreased.  At  5000  feet  elevation  the  pressure  is  but  little 
over  12  pounds  and  at  10,000  feet  the  pressure  falls  below  10 
pounds. 


Some  Principles  of  Chemistry  and  Physics.  355 

Weight  of  Gases. — The  following  table  gives  the  number  of 
cubic  feet  needed  at  sea  level  to  make  I  pound  at  62  degrees  F. 
of  the  more  usual  gases,  and  also  the  weight  in  ounces  per  cubic 
foot  at  32  degrees  F. 

At  62°  F.  13.14  cu.  ft.  =  1  Ib.  air,  and  1  cu.  ft.  =  1.29  oz.  at  32  F. 

At  02°  F.  11.89  cu.  ft.  r=  1  Ib.  O2,  and  1  cu.  ft.  =  1.44  oz.  at  32  F. 

At  02°  F.  13.53  cu.  ft.  =  1  Ib.  N2,  and  1  cu.  ft.  =  1.26  oz.  at  32  F. 

At  62°  F.  189.70  cu.  ft.  =  1  Ib.  II2,  and  1  cu.  ft.  =  0.09  oz.  at  32  F. 

At62°F.  13.55  cu.  ft.  =  l  Ib.  CO,  and  1  cu.  ft.  =  1.26  oz.  at  32  F. 

'    At62°F.  8. GO  cu.  ft.  =  1  Ib.  CO2,  and  1  cu.  ft.  =  1.98  oz.  at  32  F. 

At  02°  F.  23.32  cu.  ft.  =  1  Ib.  CH4,  and  1  cu.  ft.  =  0.73  oz.  at  32  F. 

At  62°  F.  13.46  cu.  ft.  —  1  Ib.  C2H4,  and  1  Cu.  ft.  =  1.26  oz.  at  32  F. 

The  ratio  of  weight  of  equal  volumes  of  any  gas  compared  to 
that  of  air,  is  its  specific  gravity. 

LAWS  OF  GASES. 

Although  the  fixed  gases  may  have  very  different  chemical 
compositions,  yet  in  physical  behavior  they  are  much  alike  and 
are  all  governed  by  a  distinct  set  of  laws  which  do  not  necessarily 
apply  to  other  forms  of  matter.  These  laws  define  the  interrela- 
tions of  temperature,  pressure  and  volume  and  are  known  as  the 
laws  of  gases. 

Law  of  Avogadro. — Avogadro's  hypothesis  that  equal  vol- 
umes of  all  gases  at  a  given  temperature  and  a  given  pressure 
contain  the  same  number  of  molecules,  implies  that  the  mole- 
cules of  all  gases  have  the  same  volume.  The  accuracy  of  this 
statement  is  sufficiently  well  borne  out  by  experience  to  justify  its 
application.  The  molecules  of  a  gas  are  evidently  not  restrained 
by  any  internal  cohesion  and  are  free  to  move  about  among  each 
other  with  varying  degrees  of  activity.  Their  activity  is  increased 
by  increased  temperature  of  the  gas.  The  pressure  exerted  by  a 
gas  upon  an  enclosed  space  is  supposed  to  be  the  manifestation  of 
the  continual  bombardment  of  the  enclosing  walls  by  the  rapidly 
moving  molecules.  The  pressure  naturally  depends,  therefore, 
upon  both  the  temperature  and  the  density  of  the  gas.  The  vol- 
ume, as  already  stated,  depends  upon  the  pressure  and  the  tem- 
perature. 

Law  of  Boyle. — It  was  observed  by  Boyle  in  1660  that  the 
volumes  of  perfect  gases  always  vary  inversely  as  the  pressure 
exerted  upon  them,  that  is,  a  given  weight  of  gas,  if  subjected  to 


356 


Blast  Furnace. 


double  pressure  will  be  forced  into  one-half  the  space  previously 
occupied.  In  other  words  for  a  given  weight  of  gas  the  product 
of  its  volume,  multiplied  by  its  pressure  at  any  time  is  always 
constant.  This  relationship  is  expressed  by  the  formula, 

fV=C 

which  is  perfectly  true  for  moderate  pressures.  At  very  high  pres- 
sures the  law  fails,  as  the  contraction  is  always  less  than  the 


Diagram   Illustrating  Boyle's  Law. 

amount  expected  from  the  pressure  exerted.  This  is  due  to  the 
passage  of  a  portion  of  the  gas  into  an  incompressible  condition 
whose  resistance  to  pressure  is  similar  to  that  of  a  liquid.  The 
quantity  of  the  incompressible  portion  increases  with  the  pressure. 
If  the  compressible  portion  is  called  vy  and  the  incompressible  por- 
tion b  and  the  total  volume  of  gas  is  called  V  ,  then  we  have 

V  =  v  +  b,  and  v=V  —  b. 

Substituting  this  value  of  v  in  the  formula,  pv  =  C  gives  the  ex- 
pression, 


which  is  equally  true  for  all  pressures,  since  at  low  pressures  b  is 


Some  Principles  of  Chemistry  and  Physics. 


357 


absent  and  V  =  v.  The  incompressible  portion,  designated  as  b, 
resists  pressure  like  a  liquid,  but  does  not  assume  the  form  of  a 
liquid,  however  great  the  pressure,  until  it  is  cooled  below  a  cer- 
tain critical  temperature  which  differs  for  different  gases.  For 
the  more  usual  gases  these  critical  temperatures  have  been  de- 
termined to  be  as  follows, 


CO,  = 

02"=  . 


.  .  8S°F. 
.—180°  P. 


N2  = — 231°F. 

H2  = — 390°F. 

Law  of  Qay-Lussac — It  was  observed  in  1801  by  Gay-Lussac 
that  the  volumes  of  perfect  gases,  which  are  allowed  to  expand 
freely,  vary  directly  as  their  temperatures.  Experiments  show 


9 

J^-^< 

^-^^ 

z 

0 

*t 

-V32< 

1  1  + 

.002039 

(t-3S 

^  

)J 

.  " 

^  ' 

- 

^-^ 

o 

> 

,—  — 



^^ 

^^ 

****' 

I 

^-** 

^*~ 

^~ 

.  

1 

Ho-400    -300    -200    -100       032100     200     300     400      500     600      700     800     900     1000    1100 
£§                                                   IH  TEMPERATURE   DEGREES  FAHRENHEIT 

Diagram  Illustrating  Gay-Lussac's  Law. 


that  for  every  degree  Fahrenheit  increase  in  its  temperature,  a  per- 
fect gas  will  increase  each  unit  of  the  volume  which  it  has  at  32 
degrees  F.  by  an  amount  equal  to  0.002039.  This  rate  of  in- 
crease will  double  the  volume  of  the  gas  in  490.5  degrees  F.  By 
reverse  reasoning,  it  might  be  concluded  that  at  490.5  degrees  be- 
low 32  degrees  or  — 458.5  degrees  the  gas  would  contract  to  a 
point  and  have  no  volume.  For  this  reason  — 458.5  degrees  F. 
is  designated  the  absolute  zero  of  temperature.  The  volumes  of 
gases  evidently  will  be  proportional  to  their  absolute  temperatures. 
The  volume  of  a  gas  at  any  temperature  may  be  calculated  if  its 
volume  at  any  other  temperature  is  known,  by  means  of  the  for- 
mula, 


358  Blast  Furnace. 

Vt=V32°  [l-f-a  (*-  32°)] 
where 

t  =•  temperature  in  degrees  F. 

V    —  the  volume  at  any  given  temperature. 

VS3  —  volume  at  32°  F. 

a  =  0.002039. 

It  is  only  necessary  to  reduce  the  known  volume  to  its  value  at 
32  degrees  and  substitute  this  value  in  the  equation  for  the  un- 
known volume,  thus,  for  example  : 

Let  it  be  required  to  find  the  volume  which  one  cubic  foot  of 
air  at  60  degrees  F.  will  occupy  at  1200  degrees  F. 
v  =  v&2  [i  +  a  (t  —  32)] 

whence, 

Vt 


1  +  a  (t  —  32) 
and 

1 

F33  =  —  ---  -  =  0.946  cubic  feet. 

1  +  (0.002039  X  28) 

Substituting  this  value  for  F32  in  the  formula  for  the  volume  at 
1  200  degrees,  we  have, 

T1200  —  0.946  [1  +  (0.002039  X  1168)]  =  3.199  cubic  feet, 
which  is  the  volume  at  1,200  degrees  F. 

The  same  result  may  be  attained  more  simply  by  considering 
the  volumes  proportional  to  the  absolute  temperature,  thus  : 

060  +  458.5)    :  1  =  (1,200  +  458.5)    :  x, 
whence 

x  =   3.199. 

Effusion  of  Gases.  —  The  law  of  Effusion,  announced  by 
Graham  and  Bunsen,  states  that  the  rate  of  passage  of  a  given 
volume  of  different  gases  through  a  porous  wall  or  a  small  open- 
ing is  inversely  proportional  to  the  square  root  of  the  density  of 
the  gases.  The  rate  of  transmission  is,  therefore,  a  measure  of 
density.  As  the  density  of  a  given  gas  varies  with  its  tempera- 
ture, the  rate  of  effusion  becomes  a  measure  of  any  change  of 
temperature  in  the  gas.  This  principle  forms  the  basis  of  the 
Uehling  and  Steinbart  pyrometer  for  measuring  air  blast  tem- 
peratures. 

HEAT. 

Heat  was  once  considered  to  be  a  substance  which  could  be 
added  or  subtracted  at  will,  but  it  is  now  known  to  be  only  a 
condition  of  matter.  The  present  theory  of  hea.t  is  dynamical  or 
mechanical  in  its  conception.  It  supposes  that  heat  is  the  outward 


Some  Principles  of  Chemistry  and  Physics.  359 

manifestation  of  an  increased  activity  of  motion  of  the  molecules 
of  the  substance.  Heat  and  cold  are  merely  relative  terms,  and 
are  but  manifestations  of  changes  in  intermolecular  activity.  De- 
creased activity  accompanies  increased  cold.  The  theoretical  min- 
imum of  temperature  would  represent  absolute  molecular  quies- 
cence and  is  the  absolute  zero  of  temperature. 

FUEL. 

Certain  substances  have  the  property  of  evolving  heat  when 
burned.  Many  such  substances  serve  as  fuels.  The  quantity  of 
heat  evolved  by  a  given  weight  of  combustible  and  the  tempera- 
ture attained  by  the  process  are  not  necessarily  proportional,  and 
the  ratio  varies  in  different  combustibles.  The  quantity  of  heat 
evolved  by  a  unit  quantity  of  a  combustible  is  termed  the  Calorific 
Power  of  the  substance,  and  is  measured  in  heat  units.  The  tem- 
perature attained  by  the  combustion  of  the  substance  is  measured 
in  degrees  and  is  known  as  its  Calorific  Intensity.  It  depends  not 
only  upon  the  quantity  of  heat  evolved  but  also  upon  the  rate  of 
combustion  and  the  capacity  of  the  products  of  combustion  to  ab- 
sorb the  heat.  For  example,  the  oxidation  of  wood  during  slow 
decay  releases  the  same  number  of  heat  units  as  if  the  wood  were 
cast  into  a  fire  and  burned,  but  the  calorific  intensity  attained  in 
the  two  cases  is  very  different.  The  calorific  intensity  may  be 
calculated  if  the  above  factors  are  known,  or  it  may  be  measured 
directly  by  thermometers,  pyrometers  or  any  device  which  is  af- 
fected by  changes  of  temperature. 

Determination  of  Calorific  Power. — The  calorific  power  of 
a  substance  is  determined  by  means  of  a  device  known  as  a  calori- 
meter, in  which  the  heat  developed  by  combustion  is  absorbed  by 
some  suitable  medium  and  its  quantity  measured.  The  usual 
absorbing  medium  is  water.  If  the  rise  in  temperature  is  ob- 
served, and  the  weight  of  water  is  known,  the  quantity  of  heat 
may  be  calculated.  The  amount  of  heat  which  raises  i  pound  of 
water  I  degree  F.  is  termed,  as  we  have  said,  a  British  Thermal 
Unit,  B.  T.  U.  The  calorific  power  of  many  substances  has  been 
determined  by  calorific  measurements.  Some  of  the  most  impor- 
tant are  as  follows : 


360  Blast  Furnace. 

1  pound  C  to  CO 4,450  B.  T.  U. 

1  pound  C  to  CO. 14,550  B.  T.  U. 

1  pound  CO  to  CO3 4,325  B.  T.  U. 

1    pound  II   to  IL.O 62,000  B.  T.  U. 

1  pound  II  to  steam 51,700  B.  T.  U. 

Determination  of  Calorific  Intensity. — Since  the  calorific 
intensity  of  a  given  fuel  is  the  ratio  between  its  power  to  develop 
heat  and  the  power  of  the  resulting  products  of  combustion  to 
absorb  the  heat  produced,  it  follows  that  it  can  be  found  by  simple 
calculation,  by  dividing  the  calorific  power  by  the  weight  of  the 
products  of  combustion,  multiplied  by  their  Specific  Heats.  For 
cxample,  the  calorific  intensity  of  carbon  when  burned  in  an  at- 
mosphere of  oxygen  alone  may  be  found  as  follows,  by  means 
of  the  formula  for  the  Specific  Heat  of  CO2  at  temperatures  above 
3600  degrees  F. : 

0.41*  +  0.000034 t-  =  heat  of  combustion. 
C  +  O2  =  CO2, 

by  which  14,550  B.  T.  U.  are  developed  per  pound  of  carbon,  and 
the  weight  of  the  combustion  product  CO.,,  equals  —  -  or  3.667 
pounds.  Whence, 

3.667  (0.41*  +  0.000034*2)   =  14,550, 
0.00012468*2  -f   1.50347*  =  14,550. 

Completing  the  square,  by  adding  4529  to  each  side  of  the  equa- 
tion, gives 

0.00012468*2  +  1.50347*  +  4,529  =  19,079. 
By  taking  the  square  root  we  have, 

0.01117*  -4-  67.3  =   138.1, 
whence, 

0.01117*  =  70.8, 
and, 

*  —  6,338  degrees  F. 

When,  however,  the  combustion  of  carbon  takes  place  in 
oxygen  of  the  air  with  its  accompanying  nitrogen,  the  products  of 
combustion  are  increased  by  just  that  quantity  of  nitrogen,  which, 
in  turn,  absorbs  iis  share  of  heat  developed  and  the  resulting  tem- 
perature is  correspondingly  lower.  By  means  of  the  formulas,  for 
temperatures  below  3600  degrees  F., 

0.187*  -f-  O.OOOlll*2  —  heat  developed,  and 
0.2405*  +  0.00002143*2  =  heat  developed, 

for  the  specific  heats  of  CCX  and  N2,  respectively,  the  theoretical 


Some  Principles  of  Chemistry  and  Physics.  361 

temperature  may  be  calculated.  Assuming  no  excess  of  air  to  be 
used,  then, 

C  +  02  4-  No  =  C02  +  N2, 

develops  14,550  B.  T.  U.  per  pound  of  carbon  and  the  products 
of  combustion  equal  -  ==.  3.667  pounds  CO  and  -  '  —  8.75 
pounds  N2,  whence 

3.667  (0.187*  4- 0.00011 1/2)        j    _    ,4^0 
8.75  (0.2405*  4- 0.00002143*2)  j    ~   x*'o° 
or, 

0.0004070*2  4-  0.6857* 
0.0001875*2  4-  2.1044* 

0.0005945 13  4-  2.7901*  =  14,550. 
Completing  the  square  gives, 

0.0005945*2  4-  2.7901*  +  3,272  —  17,822. 
The  square  root  equals, 

0.0244*  4-  57.2  —  133.5. 
Whence, 

0.0244*  =  76.3, 
and, 

*  —  3,127  degrees  F. 

The  theoretical  temperature  of  the  combustion  of  carbon  to 
the  condition  of  CO  in  the  presence  of  air  may  be  shown  as  fol- 
lows: 

.  C,  -f-  02'4-  N2  -  2CO  4-  N2, 

develops  4450  B.  T.  U.  per  pound  of  carbon  and  the  products  of 
combustion  are  2.333  pounds  CO  and  4.375  pounds  N2.  As  the 
heat  capacities  of  CO  and  N2  are  identical,  we  have 

6.708   (0.2405*  +  0.00002143*2)  =  4,450, 
or, 

0.00014375*2  4-  1.61327*  —  4,450. 
Completing  the  square  gives,    . 

0.00014375*2  4-  1.61327*  +  4,637  =  9,087, 
the  square  root  of  which  is, 

0.01199*  +  68.1  =  95.3. 
When  ce, 

*  =  2,270  degrees  F. 

The  theoretical  temperature  of  CO  burned  in  air  is  somewhat 
higher  than  that  accompanying  its  formation. 

2CO  4-  02  -f  N2  =  2C02  ~  N2, 

whence  it  appears  that  4325  B.  T.  U.  are  developed  per  pound  of 

00 

CO  and  the  products  of  combustion  equal  —  or  1.5714  CO2,  and 

0 

—Jii or  1.875  Mbs.  N2,  whence, 

56 


362  Blast  Furnace. 

1.5714  (0.187*  +  O.OOOllli2)         )_      oo- 
1.8750  (0.2405* +  0.00002143/2)  j   -  4'°-°' 
and, 

0.29385*  +  0.0001744*2 
0.45095  +  0.0000402/2 

0.74480*  +  0.00021 46*2  =  -1,325. 
Completing  the  square  gives, 

0.00021467-  4-  0.7448*  4  G45  ==  4,970. 
Taking  the  square  root  gives, 

0.01465*  +  25.4  =  70.5. 
*  =  3,080  degrees  F. 

In  the  case  of  hydrogen  the  product  of  the  combustion  is 
water.  At  the  temperature  of  the  reaction  the  water  exists  in  the 
form  of  steam,  which  is  a  vapor  and  not  a  fixed  gas  such  as  CO, 
CO2,  and  N2.  The  vaporization  of  the  water  renders  latent  a 
large  amount  of  the  heat  developed  by  the  combustion,  which  is 
not  given  out  unless  the  products  of  combustion  are  cooled  below 
212  degrees  F.  As  this  rarely  occurs  in  ordinary  cases  of  combus- 
tion, it  is  best  to  deduct  the  latent  heat  of  vaporization  of  steam 
from  the  total  heat  developed  and  to  treat  it  as  if  never  produced. 
It  amounts  to  about  10,300  B.  T.  U.  per  pound  of  hydrogen,  leav- 
ing a  net  heat  development  of  51,700  B.  T.  U. 

The  calorific  intensity  of  hydrogen  burned  to  the  condition  of 
steam  in  the  presence  of  an  exact  sufficiency  of  air  may  be  found 
as  follows : 

2H2  +  02  +  N2  =  2H2O  4  N2, 

by  which  51,700  B.  T.  U.  are  developed  per  pound  of  hydrogen 

and  the  products  of  combustion  are-^-  or  9.0  pounds  steam  and 

4 
105 

—  or  26.25  pounds  N2. 

4 

9.0     (0.42*  4-  0.000185*2  1  _  —  7ftfl 

26.25  (0.2405*4-0.00002143*2)  j  ~  «>-MW. 
0.0016650*2+    3.780*    . 
0.0005625*2+    6.313* 


0.0022275*2  +  10.093*  =  51,700. 
Completing  the  square  gives 

0.0022275*2  +  10.093*  +  11,449  =  63,149. 
Whence, 

0.0472*  +  107  =  251, 
and, 

*  =  3,050  degrees  F. 

It  should  be  observed,  however,  that  these  results  presuppose 
that  there  is  no  excess  of  air  over  that  theoretically  necessary  and 
that  all  of  the  heat  developed  passes  into  the  products  of  com- 


Some  Principles  of  Chemistry  and  Physics.  363 

bustion.  These  conditions  are  never  attained  in  reality,  as  there 
is  usually  an  excess  or  deficiency  of  air  and  much  heat  is  absorbed 
by  the  walls  of  the  furnace  and  lost  by  radiation  and  conduction. 
Consequently,  actual  temperatures  are  always  lower  than  theoret- 
ical results. 


APPENDIX  II. 


COST    SHEET    OF    A    SMALL    EASTERN    FURNACE    DURING    THE    FUEL 
STRINGENCY  IN    1902. 


1902. 
Tig  made. 


July. 
,  ..............   3,605 

Ores    .......................  $7.219 

Coke    .......................    6.637 

Limestone  ....................  701 

Soft  Coal  ......................  066 

Supplies  .....................  096 

Superintendent    ...............  009 

Pay   roll  .....................    1.299 

Labor   (unloading  stock)  .......  300 

Master   mechanic  ..............  010 

Materials  for  repairs  ...........  009 

Labor   for   repairs  .............  123 

Timekeepers  and  cost  clerks...      .011 

Laboratory   ..................     .036 

Reserve  fund  ..................  050 

Relining  fund  .................  100 

Insurance    .  .....  016 


August.    September.  October.  November. 
4,175  3,784  2,835  3.174 


$G.G77 
5.9S3 
.809 
.037 
.131' 
.020 
1.039 
.336 
.009 
.039 
1.138 
.010 
.030 
.050 
.100 
.013 


$7.273 
6.657 
.790 
.071 
.165 
.016 
1.153 
.194 
.010 
.056 
.160 
.010 
.033 
.050 
.100 
.015 


$6.794 
8.898 
.846 
.152 
.222 
.021 
1.398 
.285 
.013 
.048 
.279 
.017 
.047 
.050 
.100 
.020 


$6.884 
7.9£3 
.982 
.116 
.140 
.016 
1.156 
.234 
.009 
.045 
.142 
.012 
.036 
.050 
.100 
.016 


Totals $16.742 

Less    by-products 


$15.442 
.276 


$16.753 
.170 


$19.190 
.007 


$17.924 
.184 


Net  cost $16.742 

Ccst,  excluding  ore,  fuel  and  flux    2.185 


$15.166 
1.697 


$16.583 
1.863 


$19.183 
2.635 


$17.740 

1.888 


INDEX. 


Acid  constituents  of  slag 159 

Agglomeration  of  iron  ore 61 

Air  receiver 267 

Aluminum,  effect  of,  in  cast  iron...  31 

Analyses  of  iron  ore 68,  60 

Annealing,  action  of  metalloids  dur- 
ing   324 

malleable  castings 322 

Anthracite  as  a  blast  furnace  fuel.  .  73 

Baker-Neuman  stock  distributor.  . . .  108 

Ball-Norton  magnetic  separator....  58 

Banking  a  blast  furnace 152 

Base,  available,  of  flux 89 

Basic  Bessemer  pig  iron 47 

process 304 

Basic  constituents  of  slag 161 

open  hearth  process 301 

pig  iron 46 

Beehive   coke 75 

Beehive  coke  oven 76 

Bell  and  hopper 100 

Berg  hot  metal  ladle 138 

Bessemer  pig 297 

Bessemer  pig  iron 46 

Bessemer   process 294 

Bian  gas  washer 102 

Blast  furnace,  height,  effect  of 228 

limits  of  size  of 229 

lining 95 

thermal   efficiency   of 278 

Blast,  Gayley  dry 213 

heat  in  the 199 

latent  heat  of  expansion  of 217 

Blast  main 266 

moisture  in 212 

temperature,  limits  of 210 

volume   of 210 

Bleeder   101 

Blowing  down  furnace 154 

Blowing  engines 126 

Blowing  engine  valve,  Mesta.  . .  .271,  272 

Southwark   270,  271 

Blowing  in  blast  furnace 133 

Blowing  out 155 

Blowing,  power  requirement  for....  275 

Boilers,  steam 279 

Bosh  construction 256 

furnace   93 

plates  94 

size   of 249 

Breakers,   pig 137 

Break-outs    239 

Briquetting   iron   ore 

Brown  pyrometer 124 

Brown    stock    distributor 106,  107 

Buchanan  magnetic  separator 58 


Burdening  the  blast  furnace 156 

Bustle    pipe 266 

By-product   coke 77 

Calcination  of   limestone 87 

Calcination  of  ores 50 

Carbon,  absorption  of,  in  iron 22 

combined 19 

control    of 179 

deposition  in  the  blast  furnace...  190 

in  cast  iron,  effect  of  phosphorus. .  27 

in  pig  iron 18 

in  the  cupola 316 

ratio 193 

strengthening    effect    of,    in    cast 

iron    21 

Carbonic  acid,   action  of,   upon  fur- 
nace charge 190 

Carbonic     oxide,     action     of,     upon 

oxides  of  iron 185 

danger  from,  in  blowing  in 135 

Cast  house 125 

Casting  machines 139 

Castings,   chilled 318 

converted  gray 325 

effect  of  moulding  on 320 

effect  of  size  of 312 

effect  of  shape  of 312 

malleable 321 

toughened   319 

Cast  iron,  definition  of 17 

expansion   of 32 

melting  point  of 33 

shrinkage  of 32 

specific  gravity  of 

the  testing  of 35 

Cavities  in  cast  iron 

Caustic  lime  as  a  flux 87 

Cementife   20 

Charcoal   82 

reduction  of  iron  ore  by 225 

Charging,   automatic 104 

Charging  the  furnace 148 

Chilled   castings 318 

hearth    244 

Chill,  the  effect  of,  on  iron 180 

Chill  pig  bed 137 

Chimneys,  stove 118 

Cinder,    granulating 145 

ladles   145 

notch 96,  254 

Cleaning,  gas,  apparatus 102,  103 

Coke    74 

by-product 77 

production   of 81,  8 

Coke  oven,  beehive 76 

by-product 77,  78 


366 


Blast  Furnace. 


Cold  furnace,  effects  of 177 

Columns    252 

Composition  of  slag 159 

Concentration,   dry 57 

of  iron  ore 55 

Constitution  of  slag 157 

Cooling  of  cast  iron 34 

Cupola,    changes    of    composition    in 

remelting  in  the 315 

operation    of 313 

Cyanides  in  the  blast  furnace 222 

Davis-Colby   roasting   kiln 54 

Davis  pig  casting  machine 141 

Distributors,   stock 106,  108 

Dolomite  as  a  flux 88 

Downtake    101 

Driving,  rapid 232 

Dry   concentration 57 

Dust   catcher 101 

Effect  of  shock 34 

Engines,    blowing,,  valve 207 

gas    280 

Equalizers   121 

Expansion  of  cast  iron 32 

Explosion,    top 244 

Feed  water,  power  requirement  for.  .  277 

Ferrite 20 

Flux,  available  base  of 89 

effect  of  heated  gases  on 183 

requirements   for  ore 170 

requirement   for   slag 169 

Fluxes    86 

Foote  hot  blast  stove 115.  116 

Foundry    iron,   grading 308 

properties    of 309 

specifications   for 310 

Foundry  pig   iron 46 

Foundations  of  blast  furnace 252 

Fuel,  constitution   of 70 

effect  of  heated  gases  on 182 

effect  of,  in  remelting  iron 317 

requirements  for  slag 169 

valuation    of 85 

Furnace   bosh 93 

banking   152 

burden    156 

charging    148 

Fusion,  zone  of 202 

Fusibility  of  slags 161 

Gas  engines 280 

Gas  cleaning  apparatus 102,  103 

latent  heat  of  expansion  of 216 

scrubbers    102,  103 

washing 283 

Gases,  composition  of,  at  various  fur- 
nace  depths 189 

volume  of   furnace 216 

Gayley  dry  blast 213 

Gjers  roasting  kiln 54 

Gogebic  iron  range ................  64 


Grading,  pig  iron 287 

Granulating    cinder 145 

Graphitic  carbon 19 

Gray   castings,  converted 325 

Gun-iron    castings 319 

Gun,   Vaughn 147,  148 

Hearth,   blast  furnace 254 

chilled    244 

size    of 248 

Hearth  temperature,  control  of 167 

judging    175 

in    the 200 

varying    176 

Heat  developed  in  the  blast  furnace..  197 

in   the  blast 199 

lost  in  waste  gases 206 

requirements  of  the  blast  furnace.  206 

Heatings,  repeated,  effect  of 34 

Hematite 41 

Heyl    &    Patterson    pig    casting    ma- 
chine      140 

Hoisting,  power  requirement  for.  . .  .  276 

Hot  blast,  effect  of 208 

fuel  value  of 209 

Hot  blast  stoves 109,  110 

Hot  spots 238 

Howe,  diagram  illustrating  the  com- 
position   and    the    properties    of 

the  iron  series 17 

Hydrogen  as  a  reducing  agent 187 

Indicators,    stock 108,  109 

Iron  ores,  analyses  of OS.  »;<) 

production   of 63,  67 

Iron  notch 142 


Jigging  iron  ore 57 

Johnson,  effect  of  silicon  on  iron.  ...     23 

Keep,   effect   of  silicon   upon   carbon 

in  pig  iron 23 

Kennedy  hot  blast  stove 113,  114 

Kennedy-Morrison   chimney  valve...    120 

Kennedy-Reynolds   valve 272,  274 

Killeen   skimmer 144 

Koerting  gas  engine 130,  282 

Ladles,   cinder 145 

hot  metal 138 

Le  Chatelier  pyrometer 124 

Limonite    41 

Lining,  blast   furnace 95,  259 

distribution    of 237 

Low  phosphorus  pig  iron 46 

Magnetite    40 

Magnetic   separators 58 

Malleable    castings 321 

specifications    for 324 

Malleable  pig  iron 46 


Index. 


367 


Manganese,  effect  of,  on  cast  iron.  . .  20 

control    of 1 78 

in  the  cupola 315 

reduction  of -IS 

Magnesian   limestone  as  a  flux 88 

Marquette  iron  range (53 

McClure-Amsler  hot  blast  stove..  117,  IIS 

Melting,  rate  of,  pig  iron 314 

Melting  point  of  cast  iron 33 

Menne   process 24(1 

Menominee  iron  range (54 

Mesaba  iron  range (54 

Mesta  blowing  engine  valve.  ..  .271,  272 

Mesta  blowing  engine 129 

Moisture  in   blast 212 

Moulding,  effect  of,  upon  castings.  . .  320 

Moulds    32^0 

Nitrogen,  action  of,  upon  burden...  187 

Nodulizing  iron   ore 01 

Notch,   cinder 00,  254 

iron    142 

Notches,  care  of 140 

Open   hearth   process 298 

Ore,   flux  requirements  for.  .  .  . 170 

effect  of  heated  gases  on 183 

Ores,  calcination   of 50 

valuation  of  iron 43 

of    iron 39 

iron,  of  the  United   States 02 

Otto  Hoffman  coke  oven 78 

Outerbridge,  effect  of  repeated  heat- 
ing and  cooling 


Pearlite  

Pig  bed 

Pig  breakers 

Pig  casting  machines 

Pig  iron  for  the  basic  Bessemer 
process  

for  the  basic  open  hearth  process.  . 

grading  of 

sampling   . 

types    of 

uses  of 

Pillaring  

Pipes  and  cavities 

Phosphorus,  benefits  of 

control  of 

effect  upon  carbon 

effect  upon  strength  of  cast  iron.  . 

sources  of  

Plates,  bosh 

Process,  Bessemer 

open  hearth 

Power  requirement  for  blowing 

for  feed   water 

for   hoisting 

for  pumping 

Puddling  

Pumping,  power  requirement  for.... 
Pyrometers  


35 

20 
130 
137 
139 

305 

303 

287 

141 

40 

287 

239 

33 

29 

178 

27 

28 

219 

94 

294 

298 

275 

277 

270 

270 

288 

270 

122 


Receiver,   air. 207 


Remelting,    changes    of    composition 

in,  in  the  cupola 315 

Reynolds   blowing  engine 127 

Roasting  of  ores 52 

Roasting    kilns 54 

Roberts  hot  blast  stove Ill,  112 

Sampling  pig  iron 141 

Scaffolding    240 

Semi-steel  castings 319 

Semet-Solvay   coke  oven -79 

Separators,   magnetic 58 

Shaft,  dimensions  of 249 

Shell,   blast  furnace 250 

Shock,   effect  of 34 

Shrinkage  of  cast  iron 32 

Siderite   42 

Silicon,  benefits  of 24 

effects  of,  in  iron 23 

reduction    of 218 

in  the  cupola 315 

Sk'mmer,    Killeen 144 

Slag,  acid  constituents  of 159 

bask  constituents  of 101 

calculation    108 

composition 159 

constitution  of 157 

disposal  of 144 

efficiency    158 

flux  requirement  for 109 

fuel  requirement  for 109 

fusibility  of 101 

influence  of,  in  puddling 291 

physical  characteristics  of 100 

relation  of,  to  product 104 

Slipping    242 

Southwark  blowing  engine 128 

Southwark  blowing  engine  valve....   270 

Specifications  for  foundry  iron 310 

for  malleable  castings 324 

Specific  gravity  of  cast  iron 32 

Steel    conversion 293 

definition  of 10 

Stock   distributors 108 

distribution    1 50,  233 

indicators 108,  109 

Stock  house 258 

Stove,  hot  blast,  design  of 201 

efficiency   203 

valves    H9 

Stoves,  cleaning  of 152 

liot   blast 109,  110 

operation   of 151 

Strength  of  cast  iron,  effect  of  phos- 
phorus         28 

Sulphur,  effect  of,  in  cast  iron 

in  the  cupola 3 

sources  of 220 

Tapping  hole 90 

Temperature,  control  of  hearth 107 

Testing  cast  iron 

Theise'n  gas  washer. 103 

Thomas-Gilchrist    process 304 


368 


Blast  Furnace. 


Titanium 

Tod   blowing  engine 

Tod  blowing  engine  valve.... 
Top.   blast  furnace 

filling   devices , 

Top.   Kennedy   furnace 

Toughened  castings 

Tuyeres    

changing    

effect  of,  in  remelting  iron 

leaky  f 


..105 


171) 
V.M 

UT:; 

258 

104 

10(5 


236 

317 
234 


Fnit  as  p  measure  of  richness 43 

Fehling  pig  casting  machine 140 

Uehliug-Steinbart  pyrometer 123 


Valve,  blowing  engines 267 


Valve.  Kennedy-Reynolds  blowing  en- 
gine  ....:...! .272,  274 

Tod  blowhig  engine 27:2.  2i."» 

Weimer   blowing  engine 274,  27.~> 

Valves,    regulating 121 

stove    119 

Vaughn    gun 147,   148 

Vermillion   iron    range 64 

Waste  gases,  heat  lost  in 20(5 

Wedging,   prevention   of 244 

Weimer  blowing  engine  valve... 274,  275 

Wenstrom  magnetic  separator 58 

Wet  concentration  of  ore 55 

Wetherill   magnetic  separator 58 

Wrought   iron 288 

definition  of 16 

Zone  of  fusion 202 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN  INITIAL  FINE  OF  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  5O  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


MAR  25  1939 


SEP 


ocr..  4 


13 


LD  21-100m-8,'34 


r~ 


.1328 


-•» 

' 


•HBBOKH 


WMMMMMMMMI 


